System and method for impedance testing DC power sources

ABSTRACT

A method includes selecting a test waveform to inject from a first DC converter to at least one first DC power source other than a fuel cell, determining a first resulting ripple that will be generated in response to injecting the test waveform onto the battery, determining at least one offset waveform to inject from at least one second DC converter to at least one second DC power source to generate one or more second ripples which cancel the first resulting ripple, injecting the test waveform from the first DC converter to the at least one first DC power source, injecting the at least one offset waveform from the at least one second DC converter to the at least one second DC power source, and determining a characteristic of the first DC power source based at least in part on the impedance response of the first DC power source.

BACKGROUND

Information technology (“IT”) loads are often deployed in racks orcabinets that in most markets average nowadays 4-6 KW per rack.Technology is getting denser with racks going over 40 KW per rack andeven higher for High Performance Computing applications. Applications inthe range of 8-35 KW are becoming more and more popular with blades,heavy storage, and networking being integrated for mobility reasons.

Cloud computing is allowing utilization of more distributedconfigurations with better utilization of existing data centers, publicclouds, and new private clouds created in a way that is allowing optimaloperation for enterprises or the small and medium business (“SMB”)market, for example, by allowing “Everything as a Service” way ofutilization for the cloud consumer. “Infrastructure as a Service” modelsare better synchronized to the requirements of businesses, therefore,there is a need in the market for building blocks for suchinfrastructure that will allow overall faster time to market at optimalcost.

SUMMARY

According to an aspect of the present disclosure, a system contains adirect current (“DC”) bus, a first DC power source other than a fuelcell electrically connected via a first input connection to a first DCconverter, wherein the first DC converter is connected via a firstoutput connection to the DC bus, at least one second DC power sourceother than a fuel cell electrically connected via at least one secondinput connection to at least one second DC converter, wherein the atleast one second DC converter is connected via at least second outputconnection to the DC bus and wherein the first output connection and theat least one second output connection connect the first DC converter andthe at least one second DC converter to the DC bus in parallel, and aprocessor connected to the first DC converter and the at least onesecond DC converter. The processor is configured withprocessor-executable instructions to perform operations comprisingselecting a test waveform to inject onto the first input connection fromthe first DC converter to the first DC power source other than a fuelcell, determining a first resulting ripple on the first outputconnection that will be generated in response to injecting the testwaveform onto the first input connection, determining at least oneoffset waveform to inject onto the at least one second input connectionfrom the at least one second DC converter to the at least one second DCpower source other than a fuel cell such that one or more second rippleswhich will be provided to the at least one second output connectioncancel the first resulting ripple, controlling the first DC converter toinject the test waveform onto the first input connection, andcontrolling the at least one second DC converter to inject the at leastone offset waveform onto the at least one second input connection.

According to another aspect of the present disclosure, a system containsan alternating current (“AC”) bus, a first direct current (“DC”) powersource electrically connected via a first input connection to a firstinverter, wherein the first inverter is connected via a first outputconnection to the AC bus, at least one second DC power sourceelectrically connected via at least one second input connection to atleast one second inverter, wherein the at least one second inverter isconnected via at least second output connection to the AC bus andwherein the first output connection and the at least one second outputconnection connect the first inverter and the at least one secondinverter to the AC bus in parallel, and a processor connected to thefirst inverter and the at least one second inverter. The processor isconfigured with processor-executable instructions to perform operationscomprising selecting a test waveform to inject onto the first inputconnection from the first inverter to the first DC power source,determining a first resulting ripple on the first output connection thatwill be generated in response to injecting the test waveform onto thefirst input connection, determining at least one offset waveform toinject onto the at least one second input connection from the at leastone second inverter to the at least one second DC power source such thatone or more second ripples which will be provided to the at least onesecond output connection cancel the first resulting ripple, controllingthe first inverter to inject the test waveform onto the first inputconnection, and controlling the at least one second inverter to injectthe at least one offset waveform onto the at least one second inputconnection.

According to another aspect of the present disclosure, a system containsan alternating current (“AC”) bus, a first direct current (“DC”) powersource electrically connected via a first DC power source inputconnection to a first DC converter, a first inverter connected to thefirst DC converter via a first DC converter output connection andconnected to the AC bus via a first inverter output connection, and aprocessor connected to the first DC converter. The processor isconfigured with processor-executable instructions to perform operationscomprising selecting a test waveform to inject onto the first DCconverter output connection from the first DC converter to the firstinverter, controlling the first DC converter to inject the test waveformonto the first DC converter output connection, and measuring a responsefrom the inverter to the test waveform.

According to another aspect of the present disclosure, a method includesselecting a test waveform to inject from a first DC converter to atleast one first DC power source other than a fuel cell, determining afirst resulting ripple that will be generated in response to injectingthe test waveform onto the battery, determining at least one offsetwaveform to inject from at least one second DC converter to at least onesecond DC power source to generate one or more second ripples whichcancel the first resulting ripple, injecting the test waveform from thefirst DC converter to the at least one first DC power source, injectingthe at least one offset waveform from the at least one second DCconverter to the at least one second DC power source, and determining acharacteristic of the first DC power source based at least in part onthe impedance response of the first DC power source.

According to another aspect of the present disclosure, a system includesa direct current (“DC”) bus, a battery electrically connected via afirst input connection to a first DC converter, wherein the first DCconverter is connected via a first output connection to the DC bus, atleast one second DC power source electrically connected via at least onesecond input connection to at least one second DC converter, wherein theat least one second DC converter is connected via at least second outputconnection to the DC bus and wherein the first output connection and theat least one second output connection connect the first DC converter andthe at least one second DC converter to the DC bus in parallel, and aprocessor connected to the first DC converter and the at least onesecond DC converter. The processor is configured withprocessor-executable instructions to perform operations comprisingselecting a test waveform to inject onto the first input connection fromthe first DC converter to the battery, determining a first resultingripple on the first output connection that will be generated in responseto injecting the test waveform onto the first input connection,determining at least one offset waveform to inject onto the at least onesecond input connection from the at least one second DC converter to theat least one second DC power source such that one or more second rippleswhich will be provided to the at least one second output connection willcancel the first resulting ripple if the battery is charging,controlling the first DC converter to inject the test waveform onto thefirst input connection, controlling the at least one second DC converterto inject the at least one offset waveform onto the at least one secondinput connection, measuring an output on the first DC converter outputconnection, and determining if the battery is charging or dischargingbased on the measured output.

According to another aspect of the present disclosure, a method includesselecting a test waveform to inject to a battery from a first DCconverter, determining a first resulting ripple that will be generatedin response to injecting the test waveform, determining at least oneoffset waveform to inject to at least one second DC power source from atleast one second DC converter such that one or more second ripples willbe provided that will cancel the first resulting ripple if the batteryis charging, injecting the test waveform to the battery, injecting theat least one offset waveform to the at least one second DC power source,determining if the first resulting ripple has been cancelled, anddetermining if the battery is charging or discharging based on the stepof determining if the first resulting ripple has been cancelled.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a fuel cell system that can beused with the exemplary embodiments.

FIG. 2 is an isometric view of a modular fuel cell system enclosure thatcan be used with the exemplary embodiments.

FIG. 3 is a schematic process flow diagram illustrating a hot box thatcan be used with the exemplary embodiments.

FIG. 4 is an isometric view of a hot box of the modular fuel cell systemof FIG. 2.

FIG. 5 is photograph of the housing of the modular fuel cell system ofFIG. 2.

FIG. 6 is a block diagram of a system according to an embodiment.

FIGS. 7A and 7B are graphs illustrating canceling ripples on a DC busover time.

FIG. 8 is a process flow diagram illustrating an embodiment method forcanceling the ripple to a DC bus caused by a test waveform.

FIG. 9A is a block diagram of a system illustrating injected waveformsand resulting canceling ripples according to an embodiment.

FIG. 9B is a graph illustrating canceling ripples on a DC bus over timeusing the waveforms shown in FIG. 9A when a tested electrochemicaldevice is in discharge mode according to an embodiment.

FIG. 9C shows a system when electrochemical impedance spectroscopy(“EIS”) is used to detect a charging state of a battery according to anembodiment.

FIG. 9D is a graph illustrating non-canceling ripples on a DC bus overtime using the waveforms shown in FIG. 9C when an electrochemical deviceis in charging mode according to an embodiment.

FIG. 9E compares a voltage ripple on the DC bus when electromechanicaldevice is discharging to the voltage ripple when the electromechanicaldevice is charging according to an embodiment.

FIG. 10 is a block diagram of a system according to an embodiment.

FIG. 11 illustrates an embodiment method for canceling the ripple to anAC bus caused by a test waveform using the system shown in FIG. 10according to an embodiment.

FIG. 12 is a block diagram of a system according to an embodiment.

FIG. 13 illustrates an embodiment method 1300 for canceling the rippleto an AC bus caused by a test waveform using the system of FIG. 12according to an embodiment.

DETAILED DESCRIPTION

Referring to FIG. 1, one exemplary fuel cell system 100 includes a DCload 102, such as an information technology (IT) load (i.e., devicesoperating in an IT system which may include one or more of computer(s),server(s), modem(s), router(s), rack(s), power supply connections, andother components found in a data center environment), an input/outputmodule (IOM) 104, and one or more power modules 106, as described inU.S. application Ser. No. 13/937,312 incorporated herein by reference inits entirety. As shown in FIG. 1, the DC load 102 may include one ormore backup power supplies 102 a connected to grid 114.

The IOM 104 may comprise one or more power conditioning components 104 awhose input is connected to a DC bus 112 a and whose output(s) areconnected to the load 102 via a main AC bus 112 b and optionally to thegrid 114 via auxiliary AC bus 113 containing a switch 113S. The one ormore power conditioning components 104 a may include components forconverting DC power to AC power, such as a DC/AC inverter 104 a (e.g., aDC/AC inverter described in U.S. Pat. No. 7,705,490, incorporated hereinby reference in its entirety), electrical connectors for AC power outputto the grid, circuits for managing electrical transients, a systemcontroller (e.g., a computer or dedicated control logic device orcircuit), etc. The power conditioning components 104 a may be designedto convert DC power from the fuel cell modules to different AC voltagesand frequencies. Designs for 208V, 60 Hz; 480V, 60 Hz; 415V, 50 Hz andother common voltages and frequencies may be provided.

Each power module 106 cabinet is configured to house a DC power source106 a. The DC power source 106 a may include, for example, a battery.The DC power source 106 a may instead or in addition include aphotovoltaic cell, a supercapacitor or a fuel cell. One example of asuitable DC power source is a stack of solid oxide fuel cells (SOFCs).

For example, the DC power source 106 a may be a fuel cell DC powersource that includes one or more hot boxes. A hot box contains one ormore stacks or columns of fuel cells (generally referred to as“segments”), such as one or more stacks or columns of solid oxide fuelcells having a ceramic oxide electrolyte separated by conductiveinterconnect plates. Other fuel cell types, such as polymer electrolytemembrane (“PEM”), molten carbonate, phosphoric acid, etc., may also beused.

Fuel cells are often combined into units called “stacks” in which thefuel cells are electrically connected in series and separated byelectrically conductive interconnects, such as gas separator plateswhich function as interconnects. A fuel cell stack may containconductive end plates on its ends. A generalization of a fuel cell stackis the so-called fuel cell segment or column, which can contain one ormore fuel cell stacks connected in series (e.g., where the end plate ofone stack is connected electrically to an end plate of the next stack).A fuel cell segment or column may contain electrical leads which outputthe direct current from the segment or column to a power conditioningsystem. A fuel cell system can include one or more fuel cell columns,each of which may contain one or more fuel cell stacks, such as solidoxide fuel cell stacks.

The fuel cell stacks may be internally manifolded for fuel andexternally manifolded for air, where only the fuel inlet and exhaustrisers extend through openings in the fuel cell layers and/or in theinterconnect plates between the fuel cells, as described in U.S. Pat.No. 7,713,649, which is incorporated herein by reference in itsentirety. The fuel cells may have a cross flow (where air and fuel flowroughly perpendicular to each other on opposite sides of the electrolytein each fuel cell), counter flow parallel (where air and fuel flowroughly parallel to each other but in opposite directions on oppositesides of the electrolyte in each fuel cell) or co-flow parallel (whereair and fuel flow roughly parallel to each other in the same directionon opposite sides of the electrolyte in each fuel cell) configuration.

The DC power source 106 a may be connected to one or more the DC buses112 such as a split DC bus, by one or more DC/DC converters 106 blocated in module 106. The DC/DC converters 106 b may be locatedanywhere in the fuel cell system, for example in the IOM 104 instead ofthe power modules 106.

The system 100 may also optionally include an energy storage module 108including a storage device 108 a, such as a bank of supercapacitors,batteries, flywheel, etc. The storage device 108 a may also be connectedto the DC bus 112 using one or more DC/DC converters 108 b as shown inFIG. 1. Alternatively, the storage devices 108 a may be located in thepower module 106 and/or together with the IT load 102.

FIGS. 2 and 5 illustrate an exemplary modular fuel cell system describedin U.S. Pat. No. 8,440,362, incorporated herein by reference in theirentirety.

The modular system may contain modules and components described above aswell as in U.S. Pat. No. 9,190,693, and entitled “Modular Fuel CellSystem” which is incorporated herein by reference in its entirety. Themodular design of the fuel cell system enclosure 10 provides flexiblesystem installation and operation. Modules allow scaling of installedgenerating capacity, reliable generation of power, flexibility of fuelprocessing, and flexibility of power output voltages and frequencieswith a single design set. The modular design results in an “always on”unit with very high availability and reliability. This design alsoprovides an easy means of scale up and meets specific requirements ofcustomer's installations. The modular design also allows the use ofavailable fuels and required voltages and frequencies which may vary bycustomer and/or by geographic region.

The modular fuel cell system enclosure 10 includes a plurality of powermodule housings 12 (containing a fuel cell power module components 70,where the housing 12 and its components 70 are jointly labeled 106 inFIG. 1), one or more fuel input (i.e., fuel processing) module housings16, and one or more power conditioning (i.e., electrical output) modulehousings 18 (where the housing and its contents are labeled 104 andreferred to as “IOM” in FIG. 1). For example, the system enclosure mayinclude any desired number of modules, such as 2-30 power modules, forexample 6-12 power modules. FIG. 2 illustrates a system enclosure 10containing six power modules (one row of six modules stacked side toside), one fuel processing module, and one power conditioning module, ona common base 20. Each module may comprise its own cabinet or housing.Alternatively, as will be described in more detail below, the powerconditioning (i.e., IOM) and fuel processing modules may be combinedinto a single input/output module located in one cabinet or housing 14.For brevity, each housing 12, 14, 16, 18 will be referred to as “module”below.

While one row of power modules 12 is shown, the system may comprise morethan one row of modules 12. For example, the system may comprise tworows of power modules stacked back to back.

Each power module 12 is configured to house one or more hot boxes 13.Each hot box contains one or more stacks or columns of fuel cells (notshown for clarity), such as one or more stacks or columns of solid oxidefuel cells having a ceramic oxide electrolyte separated by conductiveinterconnect plates. Other fuel cell types, such as PEM, moltencarbonate, phosphoric acid, etc. may also be used.

The modular fuel cell system enclosure 10 also contains one or moreinput or fuel processing modules 16. This module 16 includes a cabinetwhich contains the components used for pre-processing of fuel, such asdesulfurizer beds. The fuel processing modules 16 may be designed toprocess different types of fuel. For example, a diesel fuel processingmodule, a natural gas fuel processing module, and an ethanol fuelprocessing module may be provided in the same or in separate cabinets. Adifferent bed composition tailored for a particular fuel may be providedin each module. The processing module(s) 16 may processes at least oneof the following fuels selected from natural gas provided from apipeline, compressed natural gas, methane, propane, liquid petroleumgas, gasoline, diesel, home heating oil, kerosene, JP-5, JP-8, aviationfuel, hydrogen, ammonia, ethanol, methanol, syn-gas, bio-gas, bio-dieseland other suitable hydrocarbon or hydrogen containing fuels. If desired,a reformer 17 may be located in the fuel processing module 16.Alternatively, if it is desirable to thermally integrate the reformer 17with the fuel cell stack(s), then a separate reformer 17 may be locatedin each hot box 13 in a respective power module 12. Furthermore, ifinternally reforming fuel cells are used, then an external reformer 17may be omitted entirely.

The modular fuel cell system enclosure 10 also contains one or morepower conditioning modules 18. The power conditioning module 18 includesa cabinet which contains the components for converting the fuel cellstack generated DC power to AC power (e.g., DC/DC and DC/AC convertersdescribed in U.S. Pat. No. 7,705,490, incorporated herein by referencein its entirety), electrical connectors for AC power output to the grid,circuits for managing electrical transients, a system controller (e.g.,a computer or dedicated control logic device or circuit). The powerconditioning module 18 may be designed to convert DC power from the fuelcell modules to different AC voltages and frequencies. Designs for 208V,60 Hz; 480V, 60 Hz; 415V, 50 Hz and other common voltages andfrequencies may be provided.

The fuel processing module 16 and the power conditioning module 18 maybe housed in one input/output cabinet 14. If a single input/outputcabinet 14 is provided, then modules 16 and 18 may be located vertically(e.g., power conditioning module 18 components above the fuel processingmodule 16 desulfurizer canisters/beds) or side by side in the cabinet14.

As shown in one exemplary embodiment in FIG. 2, one input/output cabinet14 is provided for one row of six power modules 12, which are arrangedlinearly side to side on one side of the input/output module 14. The rowof modules may be positioned, for example, adjacent to a building forwhich the system provides power (e.g., with the backs of the cabinets ofthe modules facing the building wall). While one row of power modules 12is shown, the system may comprise more than one row of modules 12. Forexample, as noted above, the system may comprise two rows of powermodules stacked back to back.

The linear array of power modules 12 is readily scaled. For example,more or fewer power modules 12 may be provided depending on the powerneeds of the building or other facility serviced by the fuel cell system10. The power modules 12 and input/output modules 14 may also beprovided in other ratios. For example, in other exemplary embodiments,more or fewer power modules 12 may be provided adjacent to theinput/output module 14. Further, the support functions could be servedby more than one input/output module 14 (e.g., with a separate fuelprocessing module 16 and power conditioning module 18 cabinets).Additionally, while in one embodiment, the input/output module 14 is atthe end of the row of power modules 12, it could also be located in thecenter of a row of power modules 12.

The modular fuel cell system enclosure 10 may be configured in a way toease servicing of the system. All of the routinely or high servicedcomponents (such as the consumable components) may be placed in a singlemodule to reduce amount of time required for the service person. Forexample, the desulfurizer material for a natural gas fueled system maybe placed in a single module (e.g., a fuel processing module 16 or acombined input/output module 14 cabinet). This would be the only modulecabinet accessed during routine maintenance. Thus, each module 12, 14,16, and 18 may be serviced, repaired or removed from the system withoutopening the other module cabinets and without servicing, repairing orremoving the other modules.

For example, as described above, the enclosure 10 can include multiplepower modules 12. When at least one power module 12 is taken off line(i.e., no power is generated by the stacks in the hot box 13 in the offline module 12), the remaining power modules 12, the fuel processingmodule 16 and the power conditioning module 18 (or the combinedinput/output module 14) are not taken off line. Furthermore, the fuelcell enclosure 10 may contain more than one of each type of module 12,14, 16, or 18. When at least one module of a particular type is takenoff line, the remaining modules of the same type are not taken off line.

Thus, in a system comprising a plurality of modules, each of the modules12, 14, 16, or 18 may be electrically disconnected, removed from thefuel cell enclosure 10 and/or serviced or repaired without stopping anoperation of the other modules in the system, allowing the fuel cellsystem to continue to generate electricity. The entire fuel cell systemdoes not have to be shut down if one stack of fuel cells in one hot box13 malfunctions or is taken off line for servicing.

Each of the power modules 12 and input/output modules 14 include a door30 (e.g., hatch, access panel, etc.) to allow the internal components ofthe module to be accessed (e.g., for maintenance, repair, replacement,etc.). According to one embodiment, the modules 12 and 14 are arrangedin a linear array that has doors 30 only on one face of each cabinet,allowing a continuous row of systems to be installed abutted againsteach other at the ends. In this way, the size and capacity of the fuelcell enclosure 10 can be adjusted with additional modules 12 or 14 andbases 20 with minimal rearranging needed for existing modules 12 and 14and bases 20. If desired, the door to module 14 may be on the siderather than on the front of the cabinet.

The door 30 may open in tandem with a substantially vertical and thensubstantially horizontal swing (e.g., “gull-wing” style). In otherwords, the door 30 opens by being moved up and then at least partiallyover the top of the enclosure 10 in a substantially horizontaldirection. The terms substantially vertical and substantially horizontalof this embodiment include a deviation of 0 to 30 degrees, such as 0 to10 degrees from exact vertical and horizontal directions, respectively.

The door 30 is mounted on to walls of the enclosure or cabinet 10 of themodule 12 or 14 with plural independent mechanical arms. In the openposition the upper portion of the door 30 may be located over theenclosure or cabinet 10 and the lower portion of the door may optionallyoverhang the opening to the enclosure 10. In this configuration, thedoor 30 provides rain and snow protection for a user when open since thelower portion of the door overhangs from the fuel cell system enclosure10. Alternatively, the entire door 30 may be located over the enclosure10 in the open position.

FIG. 3 is a schematic process flow diagram representation of module 12and the hot box 31 components showing the various flows through thecomponents, as described in more detail in U.S. Pat. No. 9,461,320,incorporated herein by reference in its entirety. In the configurationillustrated in FIG. 3, there may be no fuel and air inputs to the ATO310. External natural gas or another external fuel may not be fed to theATO 310. Instead, the hot fuel (anode) exhaust stream from the fuel cellstack(s) 39 is partially recycled into the ATO as the ATO fuel inletstream. Likewise, there is no outside air input into the ATO. Instead,the hot air (cathode) exhaust stream from the fuel cell stack(s) 39 isprovided into the ATO as the ATO air inlet stream.

Furthermore, the fuel exhaust stream is split in a splitter 3107 locatedin the hot box 1. The splitter 3107 is located between the fuel exhaustoutlet of the anode recuperator (e.g., fuel heat exchanger) 3137 and thefuel exhaust inlet of the anode cooler 3100 (e.g., the air pre-heaterheat exchanger). Thus, the fuel exhaust stream is split between themixer 3105 and the ATO 310 prior to entering the anode cooler 3100. Thisallows higher temperature fuel exhaust stream to be provided into theATO than in the prior art because the fuel exhaust stream has not yetexchanged heat with the air inlet stream in the anode cooler 3100. Forexample, the fuel exhaust stream provided into the ATO 310 from thesplitter 3107 may have a temperature of above 350 C, such as 350-500 C,for example 375 to 425 C, such as 390-410 C. Furthermore, since asmaller amount of fuel exhaust is provided into the anode cooler 3100(e.g., not 100% of the anode exhaust is provided into the anode coolerdue to the splitting of the anode exhaust in splitter 3107), the heatexchange area of the anode cooler 3100 may be reduced.

The hot box 31 contains the plurality of the fuel cell stacks 39, suchas a solid oxide fuel cell stacks (where one solid oxide fuel cell ofthe stack contains a ceramic electrolyte, such as yttria stabilizedzirconia (YSZ) or scandia stabilized zirconia (SSZ), an anode electrode,such as a nickel-YSZ or Ni-SSZ cermet, and a cathode electrode, such aslanthanum strontium manganite (LSM)). The stacks 39 may be arranged overeach other in a plurality of columns or segments.

The hot box 31 also contains a steam generator 3103. The steam generator3103 is provided with water through conduit 330 a from a water source3104, such as a water tank or a water pipe (i.e., a continuous watersupply), and converts the water to steam. The steam is provided fromgenerator 3103 to mixer 3105 through conduit 330B and is mixed with thestack anode (fuel) recycle stream in the mixer 3105. The mixer 3105 maybe located inside or outside the hot box of the hot box 31. Preferably,the humidified anode exhaust stream is combined with the fuel inletstream in the fuel inlet line or conduit 329 downstream of the mixer3105, as schematically shown in FIG. 3. Alternatively, if desired, thefuel inlet stream may also be provided directly into the mixer 3105, orthe steam may be provided directly into the fuel inlet stream and/or theanode exhaust stream may be provided directly into the fuel inlet streamfollowed by humidification of the combined fuel streams.

The steam generator 3103 is heated by the hot ATO 310 exhaust streamwhich is passed in heat exchange relationship in conduit 3119 with thesteam generator 3103.

The system operates as follows. The fuel inlet stream, such as ahydrocarbon stream, for example natural gas, is provided into the fuelinlet conduit 329 and through a catalytic partial pressure oxidation(CPOx) reactor 3111 located outside the hot box. During system start up,air is also provided into the CPOx reactor 3111 through CPOx air inletconduit 3113 to catalytically partially oxidize the fuel inlet stream.The air may be blown through the air inlet conduit 3113 to the CPOxreactor 3111 by a CPOx air blower 3114. The CPOx air blower 3114 mayonly operate during startup. During steady state system operation, theair flow is turned off (e.g., by powering off the CPOx air blower 3114)and the CPOx reactor acts as a fuel passage way in which the fuel is notpartially oxidized. Thus, the hot box 31 may comprise only one fuelinlet conduit which provides fuel in both start-up and steady statemodes through the CPOx reactor 3111. Therefore a separate fuel inletconduit which bypasses the CPOx reactor during steady state operation isnot required.

The fuel inlet stream is provided into the fuel heat exchanger (anoderecuperator)/pre-reformer 3137 where its temperature is raised by heatexchange with the stack 39 anode (fuel) exhaust streams. The fuel inletstream is pre-reformed in the pre-reformer section of the heat exchanger3137 and the reformed fuel inlet stream (which includes hydrogen, carbonmonoxide, water vapor and unreformed methane) is provided into thestacks 39 through the fuel inlet conduit(s) 321. The fuel inlet streamtravels upwards through the stacks through fuel inlet risers in thestacks 39 and is oxidized in the stacks 39 during electricitygeneration. The oxidized fuel (i.e., the anode or fuel exhaust stream)travels down the stacks 39 through the fuel exhaust risers and is thenexhausted from the stacks through the fuel exhaust conduits 323 a intothe fuel heat exchanger 3137.

In the fuel heat exchanger 3137, the anode exhaust stream heats the fuelinlet stream via heat exchange. The anode exhaust stream is thenprovided via the fuel exhaust conduit 323 b into a splitter 3107. Afirst portion of the anode exhaust stream is provided from the splitter3107 the ATO 310 via conduit (e.g., slits) 3133.

A second portion of the anode exhaust stream is recycled from thesplitter 3107 into the anode cooler 3100 and then into the fuel inletstream. For example, the second portion of the anode exhaust stream isrecycled through conduit 331 into the anode cooler (i.e., air pre-heaterheat exchanger) where the anode exhaust stream pre-heats the air inletstream from conduit 333. The anode exhaust stream is then provided bythe anode recycle blower 3123 into the mixer 3105. The anode exhauststream is humidified in the mixer 3105 by mixing with the steam providedfrom the steam generator 3103. The humidified anode exhaust stream isthen provided from the mixer 3105 via humidified anode exhaust streamconduit 3121 into the fuel inlet conduit 329 where it mixes with thefuel inlet stream.

The air inlet stream is provided by a main air blower 3125 from the airinlet conduit 333 into the anode cooler heat exchanger 3100. The blower3125 may comprise the single air flow controller for the entire system,as described above. In the anode cooler heat exchanger 3100, the airinlet stream is heated by the anode exhaust stream via heat exchange.The heated air inlet stream is then provided into the air heat exchanger(cathode recuperator 3200) via conduit 3314. The heated air inlet streamis provided from heat exchanger 3200 into the stack(s) 39 via the airinlet conduit and/or manifold 325.

The air passes through the stacks 39 into the cathode exhaust conduit324 and through conduit 324 and mixer 3801 into the ATO 310. In the ATO310, the air exhaust stream oxidizes the split first portion of theanode exhaust stream from conduit 3133 to generate an ATO exhauststream. The ATO exhaust stream is exhausted through the ATO exhaustconduit 327 into the air heat exchanger 3200. The ATO exhaust streamheats air inlet stream in the air heat exchanger 3200 via heat exchange.The ATO exhaust stream (which is still above room temperature) is thenprovided from the air heat exchanger 3200 to the steam generator 3103via conduit 3119. The heat from the ATO exhaust stream is used toconvert the water into steam via heat exchange in the steam generator3103. The ATO exhaust stream is then removed from the system via theexhaust conduit 335. Thus, by controlling the air inlet blower output(i.e., power or speed), the magnitude (i.e., volume, pressure, speed,etc.) of air introduced into the system may be controlled. The cathode(air) and anode (fuel) exhaust streams are used as the respective ATOair and fuel inlet streams, thus eliminating the need for a separate ATOair and fuel inlet controllers/blowers. Furthermore, since the ATOexhaust stream is used to heat the air inlet stream, the control of therate of single air inlet stream in conduit 333 by blower 3125 can beused to control the temperature of the stacks 39 and the ATO 310.

Thus, as described above, by varying the main air flow in conduit 333using a variable speed blower 3125 and/or a control valve to maintainthe stack 39 temperature and/or ATO 310 temperature. In this case, themain air flow rate control via blower 3125 or valve acts as a mainsystem temperature controller. Furthermore, the ATO 310 temperature maybe controlled by varying the fuel utilization (e.g., ratio of currentgenerated by the stack(s) 39 to fuel inlet flow provided to the stack(s)39). Finally the anode recycle flow in conduits 331 and 3117 may becontrolled by a variable speed anode recycle blower 3123 and/or acontrol valve to control the split between the anode exhaust to the ATO310 and anode exhaust for anode recycle into the mixer 3105 and the fuelinlet conduit 329.

As shown in FIG. 4, field replaceable power module components (PMC) 70include the hot box sub-system 13, such as the cylindrical hot box 13that is shown in FIG. 2. The hot box 13 contains the fuel cell stacksand heat exchanger assembly. The PMC 70 also includes a frame 71supporting the balance of plant (BOP) sub-system including blowers,valves, and control boards, etc (not shown for clarity) and a removablesupport 72, such as fork-lift rails, which supports the hot box and theframe. The support 72 allows the PMC 70 to be removed from the powermodule 12 cabinet as a single unit or assembly. Other configurations mayalso be used. For example, the hot box 13 may have a shape other thancylindrical, such as polygonal, etc. The support 72 may comprise aplatform rather than rails. The frame may have a different configurationor it may be omitted entirely with the BOP components mounted onto thehotbox 13 and/or the support 72 instead. The PMC 70 is dimensionallysmaller than the opening in the power module 12 (e.g., the openingclosed by the door 30). Additionally, the PMC 70 may include one or morevents 81 for exhausting/ventilating gas, such as air, from within thePMC and module 12 to the outside environment. The PMC 70 may alsoinclude one or more ventilation fans or blowers 80, such as aventilation fan driven by an alternating current motor that may forcegas, such as air and/or ATO exhaust, out of the PMC 70, such as out ofthe one or more vents 81.

To maximize the efficiency and/or longevity of fuel cell stacks, such asthe fuel stacks within power module 12 discussed above, proper operatingconditions must be maintained. For example, inefficient operation mayresult if too much or too little fuel is used by the fuel system, or iftemperatures of the individual fuel cells of a fuel cell stack deviatefrom a preferred temperature range. In order to maintain properoperating conditions, it is desirable to continually monitor and adjustthe fuel cell system, its support equipment (e.g., support equipmentsuch as blowers, pumps, valves, etc.), and peripheral devices connectedto the fuel cell system.

The systems, methods, and devices of the various embodiments enableelectrochemical impedance spectroscopy (“EIS”) (also called AC impedancespectroscopy) to be performed on electrochemical devices by powerelectronics connecting the electrochemical devices in parallel to acommon load and/or bus. Electrochemical devices may include fuel cellstack segments, battery cells, electrolysis cells, electrochemicalpumping cells (e.g., hydrogen separators), or any other device that maybe monitored by EIS.

EIS enables the overall impedance of an electrochemical device to bedetermined by measuring a voltage or current across the electrochemicaldevice at varying sampling frequencies. A testing waveform selected toachieve the varying sampling frequencies, such as a waveform withoscillations of approximately 1 Hz, may be generated on a line connectedto the electrochemical device, for example by rapid switching of theline to load and unload the electrochemical device, thereby injectingthe test waveform into the electrochemical device. The testing waveformmay be a sine wave or other type wave selected to achieve desiredsampling frequencies. A voltage or current and resulting phase angle ofthe electrochemical device may be determined at each of the samplingfrequencies, and using EIS converted into impedances.

Results of the EIS procedure (e.g., the impedance at varyingfrequencies) may be graphically represented using a Nyquist plot or Bodeplot and characteristics of the electrochemical device may be determinedbased on the impedance response of the electrochemical device. Bycomparing the impedance response of the electrochemical device beingmeasured to known signatures of impedance responses of electrochemicaldevices with known characteristics, the characteristics of the measureddevice may be identified. Characteristics of the electrochemical devicethat may be determined based at least in part on the impedance responseinclude fuel conditions (e.g., fuel utilization rate), air conditions(e.g., an air utilization rate), catalyst conditions (e.g., cracks inanode catalyst coatings), and water conditions (e.g., PEM fuel cellmembrane water flooding). Based on the characteristics of theelectrochemical device a setting of the electrochemical device may beadjusted. For example, based on the fuel utilization rate and/or waterflow rate, a fuel flow and/or water flow into the fuel inlet streamsetting for fuel provided to the electrochemical device may be adjusted.Additionally, determined characteristics of the electrochemical devicemay be compared to a failure threshold, and when the characteristicsexceed the failure threshold, a failure mode of the electrochemicaldevice may be indicated, such as a fuel starvation state, a catalystpoisoning state, or a water flooding state.

FIG. 6 is a block diagram of a system 600 according to an embodiment.The system 600 may include four electrochemical devices 602, 604, 606,and 608. For example, the electrochemical devices 602, 604, 606, and 608may each be a battery or a fuel cell stack segments of fuel cells whichmay constitute a portion 106 a of power module 106. Any suitable batterymay be used as an electrochemical device, as described herein. Examplesinclude lithium ion batteries, aluminum ion batteries, nickel cadmiumbatteries, nickel zinc batteries, zinc ion batteries, polymer-basedbatteries, and alkaline batteries. Any battery suitable for a powersystem, particularly an uninterruptable power system or power backupsystem, may be used in embodiments disclosed herein.

Each electrochemical device 602, 604, 606, and 608 may be electricallyconnected via a respective input connection 640, 642, 644, and 646 to arespective one of power electronics 610, 612, 614, and 616. Each inputconnection 640, 642, 644, and 646 may comprise a respective positiveinput connection 640 a, 642 a, 644 a, and 644 b as well as a respectivenegative input connection 640 b, 642 b, 644 b, and 646 b. In operation,the electrochemical devices 602, 604, 606, and 608 may output DCvoltages to their respective power electronics 610, 612, 614, and 616via their respective input connections 640, 642, 644, and 646.

The power electronics 610, 612, 614, and 616 may be DC to DC converters,for example 380 volt 23 amp DC to DC converters. The power electronics610, 612, 614, and 616 may be each include controllers 630, 632, 634,and 636, respectively, each connected, wired or wirelessly, to a centralcontroller 638. The controllers 630, 632, 634, and 636 may includeprocessors configured with processor-executable instructions to performoperations to control their respective power electronics 610, 612, 614,and 616, and the controller 638 may be a processor configured withprocessor-executable instructions to perform operations to exchange datawith and control the operations of power electronics 610, 612, 614, and616 via their respective controllers 630, 632, 634, and 636. Via theconnections A, B, C, and D between the controllers 630, 632, 634, 636connected to the power electronics 610, 612, 614, and 616 and controller638, the controller 638 may be effectively connected to the powerelectronics 610, 612, 614, and 616 and control the operations of thepower electronics 610, 612, 614, and 616.

The power electronics 610, 612, 614, and 616 may be connected inparallel to a DC bus 618 by their respective output connections 620,622, 624, and 626. In an embodiment, the DC bus 618 may be a three phasebus comprised of a positive line 618 a, a neutral line 618 b, and anegative line 618 c, and the respective output connections 620, 622,624, and 626 may include respective positive output connections 620 a,622 a, 624 a, and 626 a, respective neutral output connections 620 b,622 b, 624 b, and 626 b, and respective negative output connections 620c, 622 c, 624 c, and 626 c. In operation, the power electronics 610,612, 614, and 616 may output DC voltages to the bus 618 via theirrespective output connections 620, 622, 624, and 626. In an embodiment,power electronics 610, 612, 614, and 616 may be three phase convertersconfigured to receive positive and negative DC inputs from theirrespective electrochemical devices 602, 604, 606, and 608 and outputpositive DC, negative DC, and neutral outputs to the bus 618 via theirrespective positive output connections 620 a, 622 a, 624 a, and 626 a,respective neutral output connections 620 b, 622 b, 624 b, and 626 b,and respective negative output connections 620 c, 622 c, 624 c, and 626c. In an alternative embodiment, power electronics 610, 612, 614, and616 may each be comprised of dual two phase converters. The positiveoutput of the first of the two phase converters may be connected to thepositive line 618 a of the bus 618 and the negative output of the secondof the two phase converters may be connected to the negative line 618 cof the bus 618. The negative output of the first of the two phaseconverters and the positive output of the second of the two phaseconverters may be connected together to the neutral line 618 b of thebus 618.

In an embodiment, the power electronics 610, 612, 614, and 616 may eachbe configured to perform EIS monitoring of their respectiveelectrochemical device 602, 604, 606, and 608. Controller 638 may selecta test waveform for use in EIS monitoring for one of the electrochemicaldevices 602, 604, 606, or 608, and may control that power electronics610, 612, 614, or 616 of that electrochemical device 602, 604, 606, or608 to inject the selected test waveform onto the respective inputconnection 640, 642, 644, or 646. For example, the controller 638 maysend an indication of the selected test waveform to the controller 630of power electronics 610 to cause opening and closing of a switch at thepower electronics 610 to generate the selected test waveform via pulsewidth modulation on the input connection 640 connected to theelectrochemical device 602. The power electronics 610, 612, 614, or 616injecting the test waveform may be configured to monitor the resultingimpedance response of its respective electrochemical device 602, 604,606, or 608, and via its respective controller 630, 632, 634, or 636 mayoutput an indication of the monitored impedance response to thecontroller 638. Continuing with the preceding example, power electronics610 may monitor the impedance response on the input connection 640 tothe electrochemical device 602 and the controller 630 may indicate theimpedance response of electrochemical device 602 to the controller 638.

Controller 638 may use the impedance response determined by EISmonitoring of an electrochemical device 602, 604, 606, 608 to determinea characteristic of that electrochemical device 602, 604, 606, 608 andmay adjust a setting of the system 600 based on the determinedcharacteristic. The controller 638 may compare the impedance responsedetermined by EIS monitoring of an electrochemical device 602, 604, 606,608, such as a plot of the impedance response and/or stored impedancevalues, to impedance responses stored in a memory, such as stored plotsof impedance responses and/or stored impedance values, of similarelectrochemical devices correlated with known characteristics. Thecontroller 638 may compare the impedance response determined by EISmonitoring of an electrochemical device 602, 604, 606, 608 to the storedimpedance responses in any manner to identify matches between theimpedance responses determined by EIS monitoring of an electrochemicaldevice 602, 604, 606, 608 and the stored impedance responses.

When the controller 638 determines a match (e.g., identically or withinsome predetermined variance value) between the impedance responsedetermined by EIS monitoring of an electrochemical device 602, 604, 606,608 and a stored impedance response, the controller 638 may determinethe characteristic correlated with the stored impedance response to bethe characteristic of the respective electrochemical device 602, 604,606, 608.

For example, controller 638 may determine an impedance variance withfrequency for a battery. In particular, higher battery impedance in thelower frequencies may indicate a sign of lower capacity and/or higherinternal resistance. Controller 638 can also use EIS to measure otherproperties of a battery, including its state of charge (SoC), state ofhealth (SoH), overall battery lifetime, and diagnose if the batteryincludes malfunctioning or underperforming cells.

In order to assess the battery's SoH, controller 638 may compare theimpedance behavior measured by EIS for the battery against a knownimpedance profile for the battery when the battery is new or in properworking order. Comparing the measured impedance behavior via EIS againstthe known impedance profile for the battery may reveal problems such asdiminished capacity, and narrow voltage output window, degradationcurrent rating, an increase in internal impedance (which may indicatefurther problems with the battery such as degraded electricalconnections, leaks, degradation of the of electrolytes, etc.). Theimpedance measurement may also show that the battery is reaching the endof its cycle life, e.g., by showing a relatively high impedance acrossall frequencies.

When a test waveform is injected on an input connection 640, 642, 644,or 646 by a respective power electronics 610, 612, 614, or 616 toperform EIS monitoring, a ripple on the respective output connection620, 622, 624, or 626 may occur. If unaccounted for, the resultingripple from the power electronics 610, 612, 614, or 616 performing EISmonitoring may cause an undesired ripple on the DC bus 618. To prevent aripple on the DC bus 618, the ripple from the power electronics 610,612, 614, or 616 performing EIS monitoring may be offset or canceled byother ripples injected into the DC bus 618. In an embodiment, the otherripples may be generated by one or more of the other power electronics610, 612, 614, or 616 not performing EIS monitoring.

The ripples from one or more of the other power electronics 610, 612,614, or 616 not performing EIS monitoring may be generated bycontrolling the one or more of the other power electronics 610, 612,614, or 616 not performing EIS monitoring to inject an offset waveforminto their respective input connections 640, 642, 644, or 646. Theoffset waveform or waveforms may be selected by the controller 638 suchthat the ripples on the respective output connections 620, 622, 624, or626 generated in response to injecting the offset waveform or waveformscancels the ripple caused by the power electronics 610, 612, 614, or 616performing EIS monitoring when the waveforms are summed at the DC bus618. In another embodiment, ripples may be injected into outputconnections 620, 622, 624, or 626 from devices other than the powerelectronics 610, 612, 614, or 616 to cancel the ripple caused by thepower electronics 610, 612, 614, or 616 performing EIS monitoring whenthe waveforms are summed at the DC bus 618. For example, a waveformgenerator may be connected to output connections 620, 622, 624, or 626to inject canceling ripples in response to EIS monitoring.

FIG. 7A is a graph illustrating canceling ripples on a DC bus over time.A test waveform injected onto an input connection of an electrochemicaldevice by a power electronics may result in a ripple 702 sent from thepower electronics injecting the test waveform toward a DC bus. An offsetwaveform injected onto an input connection of another electrochemicaldevice by another power electronics may result in a ripple 704 sent fromthat power electronics injecting the offset waveform toward the DC bus.The offset waveform may be selected such that the ripple 704 is 180degrees out of phase with the ripple 702. The power electronics may beconnected to the DC bus in parallel and the sum of the ripple 702 andthe ripple 704 may cancel each other out such that the sum of thewaveforms is the desired DC voltage 706 on the DC bus.

FIG. 7B is another graph illustrating canceling ripples on a DC bus overtime using more than one offsetting waveform. As discussed above, a testwaveform injected onto an input connection of an electrochemical deviceby a power electronics may result in a ripple 702 sent from the powerelectronics injecting the test waveform toward a DC bus.

Three other power electronics may be used to generate offset waveformsinjected onto input connections of three other electrochemical devices.The first offset waveform injected onto an input connection of a firstother electrochemical device by the first other power electronics mayresult in a ripple 708 sent from that first other power electronicsinjecting the offset waveform toward the DC bus. The second offsetwaveform injected onto an input connection of a second otherelectrochemical device by the second other power electronics may resultin a ripple 710 sent from that second other power electronics injectingthe offset waveform toward the DC bus. The third offset waveforminjected onto an input connection of a third other electrochemicaldevice by the third other power electronics may result in a ripple 712sent from that third other power electronics injecting the offsetwaveform toward the DC bus. The three offset waveforms may be selectedsuch that the sum of the ripples 708, 710, and 712 may cancel ripple 702such that the sum of the waveforms is the desired DC voltage 706 on theDC bus. While illustrated in FIGS. 7A and 7B as one generated offsettingripple 704 or three offsetting ripples 708, 710, 712 with the samefrequency as the ripple 702, more or less offsetting ripples, withdifferent waveforms, different frequencies, phases, amplitudes, etc. maybe generated and injected toward the DC bus as long as the total of anyoffsetting ripples plus the ripple 702 sent from the power electronicsinjecting the test waveform toward the DC bus results in the desired DCvoltage 706 on the DC bus with no ripple.

FIG. 8 illustrates an embodiment method 800 for canceling the ripple toa DC bus caused by a test waveform using system 600. In an embodiment,the operations of method 800 may be performed by a controller, such ascontroller 638. The operations of method 800 are discussed in terms ofbatteries, fuel cell stack segments, and DC converters, but batteries,fuel cell stack segments, and converters are used merely as examples.Other electrochemical devices and/or other power electronics may be usedin the various operations of method 800.

In block 802 the controller 638 may select an electrochemical device,such as a battery, from a plurality of electrochemical devices forimpedance testing. For example, the electrochemical device may beselected based on a testing protocol governing when and in what orderelectrochemical devices may be tested. In block 804 the controller 638may select a test waveform. The test waveform may selected to generatenecessary oscillations for EIS monitoring, such as oscillations ofapproximately 1 Hz.

In block 806 the controller 638 may determine a resulting ripple to becaused by the selected test waveform. As discussed above, the resultingripple may be the ripple output to the DC bus from the DC converterinjecting the test waveform. In block 808 the controller 638 mayidentify the remaining electrochemical devices. The remainingelectrochemical devices may include batteries, fuel cell stack segments,supercapacitors, etc. Alternatively, other remaining DC power sources,such as photovoltaic cells or thermoelectric generators, may beidentified. The remaining electrochemical devices may be theelectrochemical devices not selected for impedance testing. In block 810the controller 638 may select a portion of the identified remainingelectrochemical devices. In an embodiment, the selected portion may beall identified remaining batteries and fuel cell stack segments. Inanother embodiment, the selected portion may be less than all identifiedremaining batteries and fuel cell stack segments, such as only a singleidentified remaining fuel cell stack segment.

In block 810 the controller 638 may determine an offset waveform foreach selected remaining fuel cell stack segment such that a sum of eachresulting ripple to be caused by the respective determined offsetwaveforms for each selected remaining electrochemical devices cancelsthe determined resulting ripple to be caused by the selected testwaveform. In an embodiment, each offset waveform may be generated suchthat the resulting ripple is the same, such as one, two, three or moreequal ripples that together cancel the ripple from the test waveform. Inanother embodiment, each offset waveform may be generated such that theresulting ripples are different, such as two, three, or more differentripples that together cancel the ripple from the test waveform.

In block 812 the controller 638 may control the DC converter of theelectrochemical device selected for impedance testing to inject the testwaveform into the selected electrochemical device. For example, thecontroller 638 may send control signals to a controller (e.g., 630, 632,634, or 636) of the DC converter to cause the converter to perform pulsewidth modulation to generate the test waveform on an input connection tothe electrochemical device. In block 814 the controller 638 may controlthe DC converters of each selected remaining electrochemical device toinject the offset waveform for each selected remaining electrochemicaldevices into each respective electrochemical device. For example, thecontroller 638 may send control signals to the controllers (e.g., 630,632, 634, and/or 636) of the DC converters to cause the converters toperform pulse width modulation to generate the offset waveforms on aninput connection to their respective electrochemical devices. Theoperations of method 800 performed in blocks 812 and 814 may occursimultaneously, such that the test waveform and offset waveforms areinjected at the same time resulting in ripples being output from thevarious DC converters that cancel each other out resulting in a thedesired DC voltage on the DC bus.

In block 816 the controller 638 may control the DC converter of the DCpower source selected for impedance testing to monitor the impedanceresponse of the DC power source in response to the injected testwaveform.

In block 818 the controller 638 may determine a characteristic of theelectrochemical device selected for impedance testing based at least inpart on the impedance response. As discussed above, the controller mayuse EIS monitoring to plot the real and imaginary parts of the measuredimpedances resulting from the injected test waveform and compare theplotted impedances to the known signatures of impedance responses ofelectrochemical devices with known characteristics. The known signaturesof impedance responses of the electrochemical devices with knowncharacteristics may be stored in a memory available to the controller.The stored known signatures of impedance responses of theelectrochemical devices with known characteristics may be plots of thereal and imaginary parts of the measured impedances of healthy fuelelectrochemical devices and damaged/degraded electrochemical devicesderived from testing healthy (i.e., undamaged/undegraded) anddamaged/degraded electrochemical devices with various forms of damage(e.g., anode cracking of fuel cells) and/or degradation (e.g.,degradation of the electrolyte of a fuel cell). The knowncharacteristics may be correlated with the plots of the real andimaginary parts of the measured impedances stored in the memory. Bymatching the measured impedances to the known signatures of impedanceresponses, the current characteristics or state of the electrochemicaldevice may be determined as those characteristics correlated with thematching known signature of impedance response.

In optional block 820 the controller 638 may indicate a failure modebased on the determined characteristic exceeding a failure threshold.For example, if the determined characteristic exceeds a failurethreshold, then a failure mode may be indicated. For example, for a fuelcell, a failure mode may be a fuel starvation state, catalyst damageand/or poisoning state, or a water flooding. In optional block 822 thecontroller 638 may adjust a setting of the electrochemical device systembased on the determined characteristic. For example, the controller 638may adjust (e.g., increase or decrease) drawn current fromelectrochemical devices or shut off of the electrochemical devices basedon the determined characteristic. In this manner, impedance testing,such as EIS monitoring, may be used in a fuel cell system to adjust theoperation of the electrochemical device system based on currentcharacteristics of the electrochemical devices.

FIG. 9A is a block diagram of the system 600 described above withreference to FIG. 6, illustrating injected waveforms 902, 906, 910, and914 and resulting canceling ripples 904 a, 908, 912, and 916 accordingto an embodiment. Note that FIG. 9A assumes that, if any DC powersources 602-608 are batteries, then the batteries are in a state ofdischarging rather than a charging state. The case in which anelectrochemical device is charging is dealt below in the context ofFIGS. 9C and 9D.

A test waveform 902 may be injected into the input connection 640resulting in a test ripple 904 a on the output connection 620 to the DCbus 618. An offset waveform 906 may be injected into the inputconnection 642 resulting in an offset ripple 908 on the outputconnection 622 to the DC bus 618. An offset waveform 910 may be injectedinto the input connection 644 resulting in an offset ripple 912 on theoutput connection 624 to the DC bus 618. An offset waveform 914 may beinjected into the input connection 646 resulting in an offset ripple 916on the output connection 626 to the DC bus 618. The sum of the ripples904, 908, 912, and 916 may be such that steady DC voltage 918 a withouta ripple occurs on the DC bus 618 despite AC ripples occurring on theoutput connections 620, 622, 624, and 626. While the sum of the ripples904, 908, 912, and 916 may be such that steady DC voltage 918 a withouta ripple results on the DC bus 618, the sum of the offset waveforms 906,910, and 914 and the test waveform 902 need not equal zero. The offsetripples 908, 912, and 916 may all be the same or may be different. Forexample, offset ripple 908 may be a larger ripple than offset ripples912 and 916. Additionally, whether or not the offset ripples 908, 912,and 916 are the same or different, the offset waveforms 906, 910, and914 may not be the same. While three offset waveforms 906, 910, and 914and their resulting offset ripples 908, 912, and 916 are illustrated,less offset waveforms and offset ripples, such as only two offsetwaveforms and resulting offset ripples or only one offset waveform andone resulting offset ripple, may be generated to offset the test ripple904 a. Alternatively, DC power sources 602, 604, 606, and 608 may alsocomprise non-electrochemical DC power sources, such as solar cells orthermoelectric devices. Each DC power source 602-608 has a separate,respective, dedicated power electronic device 610-616 which injects awaveform into the respective DC power source 602-608.

In one embodiment, each DC power source other than a fuel cell basedpower source contains a dedicated, separate, respective, DC/DC converterwhich injects either a test waveform or an offset waveform into the DCpower source. The DC power source can be a battery, supercapacitor,photovoltaic cell or thermoelectric device in this embodiment. The testwaveform causes a test ripple on the output connection from the DC/DCconverter sending the test waveform. The offset waveform(s) cause(s) anoffset or complimentary ripple on the output connection from the DC/DCconverter(s) sending the offset waveform(s). The offset ripples offsetand cancel the test ripple, while the complementary ripple(s)superimpose on the test ripple and increase the amplitude of the testripple, as will be described below in more detail.

In an alternative embodiment, the offset ripples 908, 912, and/or 916may be generated by other devices, such as waveform generators,connected to output connections 622, 624, and 626 and controlled by thecontroller 638, rather than the power electronics 612, 614, and/or 616.The offset ripples 908, 912, and/or 916 may be generated by the otherdevices such that the sum of the ripples 904 a, 908, 912, and 916 may bethe steady DC voltage 918 a without a ripple on the DC bus 618.Additionally, combinations of ripples generated by the power electronics612, 614, and/or 616 and the other devices, such as additional waveformgenerators, may be used to cancel the ripple 904 a resulting in thesteady DC voltage 918 a without a ripple on the DC bus 618.

FIG. 9B is a graph illustrating canceling ripples on a DC bus over timeusing the waveforms shown in FIG. 9A when the DC power source, such asan electrochemical device 602 is in discharge or power generation mode.As discussed above, test waveform 902 is injected by power electronics(e.g., DC/DC converter) 610 onto an input connection 640 a to DC powersource 602 resulting in test ripple 904 a toward the DC bus 618.

Three other power electronics (e.g., DC/DC converter) 612, 614, and 616generate offset waveforms 906, 910, and 914, respectively, injected ontoinput connections 642 a, 644 a, and 646 a of three other DC powersources, such as electrochemical devices 604, 606, and 608. The firstoffset waveform 906 may result in a ripple 908 sent toward the DC bus.The second and third offset waveforms 910 and 914 may result in ripples912 and 916, respectively, sent toward the DC bus 618. The three offsetwaveforms 906, 910, and 914 may be selected such that the sum of theripples 908, 912, and 916 may cancel ripple 904 a such that the sum ofthe waveforms is the desired DC voltage 918 a on the DC bus with noripple.

FIG. 9C shows system 600 when EIS is used to detect a charging state ofa battery. More specifically, in FIG. 9C, DC power source 602 is anelectrochemical energy storage device, such as a battery that may be ineither a charging state or a discharging state. When electrochemicalenergy storage device 602 is in the charging state, current flows fromDC/DC converter 610 to electrochemical device 602 via input connection640 a along the direction 950 a. Conversely, when electrochemical energystorage device 602 is in the discharge state, current flows in theopposite direction 950 b. As discussed above, FIGS. 9A and 9B show theresult when electrochemical energy storage device 602 is in thedischarge state.

The description of the functioning of system 600 when electrochemicalenergy storage device 602 is in the charging state is similar to thesituation when the electrochemical energy storage device 602 is in thedischarging state (i.e., the description in the context of FIG. 9A).Therefore, only the differences are described. Specifically, ripple 904b shown in FIG. 9C produced by providing test waveform 902 toelectrochemical energy storage device 602 while in the charging state isin the opposite direction (i.e., 180 degrees out of phase) compared tothe ripple 904 a (FIG. 9A) produced by applying the same test waveformto 602 when discharging.

Despite that electrochemical energy storage device 602 is in chargingmode, the controller 638 controls electrochemical devices 604, 606, and608 to generate compensatory ripples 908, 912, and 916 for cancelling aripple 904 b generated based on test signal 902 when electrochemicalenergy storage device 602 is in charging mode. Therefore, as shown inFIG. 9C, compensatory ripples 908, 912, and 916 in charging mode areidentical to the offset compensatory ripples 908, 912, and 916 indischarging mode (FIG. 9A). Such compensatory ripples 908, 912, and 916may not cancel ripple 904 b when the electrochemical energy storagedevice 602 is in charging mode. Therefore, detecting a (non-cancelled)voltage ripple 918 b on DC bus 618 can be used as an indication thatelectrochemical energy storage device 602 is in charging mode. FIG. 9Dexplains in more detail how a non-cancelled voltage ripple 918 c canindicate charging mode in the tested electrochemical energy storagedevice 602.

FIG. 9D is a graph illustrating non-canceling ripples on a DC bus overtime using the waveforms shown in FIG. 9C when electrochemical energystorage device 602 is in charging mode. As discussed above, testwaveform 902 is injected by power electronics 610 onto an inputconnection 640 a to electrochemical energy storage device 602. Thisresults in ripple 904 b toward the DC bus 618.

Three other power electronics 612, 614, and 616 generate offsetwaveforms 906, 910, and 914, respectively, injected onto inputconnections 642 a, 644 a, and 646 a of three other electrochemicaldevices 604, 606, and 608, e.g., fuel cell segments or other batteries.The first offset waveform 906 may result in a ripple 908 sent toward theDC bus. The second and third offset waveforms 910 and 914 may result inripples 912 and 916, respectively, sent toward the DC bus 618. Thesethree offset waveforms 906, 910, and 914 may be selected such that thesum of the ripples 908, 912, and 916 would cancel the ripple created bytest waveform 902 when electrochemical energy storage device 602 is indischarge mode. When electrochemical energy storage device 602 is incharging mode, however, such compensatory ripples 908, 912, and 916 willnot cancel ripple 904 b. Instead, compensatory ripples 908, 912, and 916will add to (i.e., superimpose on) ripple 904 b when the ripples are inphase, as shown in FIG. 9D, to result in an increased amplitude of DCvoltage ripple 918 b on the DC bus. The increased amplitude of DCvoltage ripple 918 b on the DC bus can be taken as an indication thatthe tested electrochemical energy storage device 602 is operating in adischarge mode.

FIG. 9E compares the voltage ripple 918 a on the DC bus whenelectrochemical energy storage device 602 is discharging to the voltageripple 918 b in which electrochemical energy storage device 602 ischarging. As shown in FIG. 9E, the presence of ripple 918 b is easilydistinguished from the output voltage 918 a which lacks a ripple andwhich occurs when compensatory ripples 908, 912, and 916 cancel a ripple904 a created when electrochemical energy storage device 602 is incharging mode. Therefore, the presence of the ripple at the DC bus 618can be used as a means to distinguish between the state when the testedelectrochemical energy storage device 602 is charging or discharging.

FIG. 10 is a block diagram of a system 1000 according to an embodiment.FIG. 10 shows system 1000 including two DC power sources, such aselectrochemical devices 602 and 604 as part of an array of “n” DC powersources. In the description that follows, merely for the purpose ofillustration, only two DC power sources 602 and 604 are discussed. It isto be understood, however, that system 1000 may include any suitablenumber of DC power sources (e.g., the four electrochemical devices 602,604, 606, and 608 and/or other DC power sources, e.g., solar cells orthermoelectric devices shown in FIG. 6). It is to be further understoodthat the various output ripples discussed below as being generated bythe two DC power sources may vary according to the number of DC powersources.

As in system 600, DC power sources 602, 604 . . . n in system 1000 mayeach be a battery, supercapacitor, a fuel cell stack segments of fuelcells, photovoltaic cells, or thermoelectric devices which mayconstitute a portion 106 a of power module 106. System 1000, however,provides the separate, dedicated inverters 1010 and 1012 for each DCpower source 602, 604 . . . n. In addition, DC bus 618 is replaced by ACbus 1018. The DC/DC converters 610, 612 may be omitted or present inthis embodiment.

DC power sources 602 and 604 in system 1000 may be electricallyconnected via a respective input connection 640 and 642 to a respectiveone of the inverters 1010 and 1012. Each input connection 640 and 642may comprise a respective positive input connection 640 a and 642 a aswell as a respective negative input connection 640 b and 642 b. Inoperation, the DC power sources 602 and 604 may output DC voltages totheir respective inverters 1010 and 1012 via their respective inputconnections 640 and 642. Inverters 1010 and 1012 may then convert the DCoutput voltages to AC output and provide the AC output to AC bus 1018.

Inverters 1010 and 1012 may each include controllers 1030 and 1032 whichare connected, wired or wirelessly, to central controller 1038. Thecontrollers 1030 and 1032 may include processors configured withprocessor-executable instructions to perform operations to control theirrespective inverters 1010 and 1012, and the controller 1038 may be aprocessor configured with processor-executable instructions to performoperations to exchange data with and control the operations of inverters1010 and 1012 via their respective controllers 1030 and 1032. Via theconnections A and B between the controllers 1030 and 1032 connected tothe inverters 1010 and 1012 and controller 1038, the controller 1038 maybe effectively connected to the inverters 1010 and 1012, and control theoperations of the inverters 1010 and 1012. The inverters 1010 and 1012may be connected in parallel to the AC bus 1018 by their respectiveoutput connections 620 and 622. (e.g., AC buses).

In an embodiment, the AC bus 1018 may be a three phase bus comprised ofa positive line 1018 a, a neutral line 1018 b, and a negative line 1018c, and the respective output connections 620 and 622, may includerespective positive output connections 620 a and 622 a, respectiveneutral output connections 620 b and 622 b, and respective negativeoutput connections 620 c and 622 c. Alternatively, the AC bus 1018 maybe a single phase, two phase, or a four phase bus. In an embodiment,inverters 1010 and 1012 may be three phase inverters configured toreceive positive and negative DC inputs from their respective DC powersources 602 and 604 and output positive AC, negative AC, and neutraloutputs to the bus 1018 via their respective positive output connections620 a and 622 a, respective neutral output connections 620 b and 622 b,and respective negative output connections 620 c and 622 c. In analternative embodiment, inverters 1010 and 1012 may each be comprised ofdual two phase inverters. The positive output of the first of the twophase inverters may be connected to the positive line 1018 a of the bus1018 and the negative output of the second of the two phase convertersmay be connected to the negative line 1018 c of the bus 1018. Thenegative output of the first of the two phase inverters and the positiveoutput of the second of the two phase inverters may be connectedtogether to the neutral line 1018 b of the bus 1018.

In an embodiment, the inverters 1010 and 1012 may each be configured toperform EIS monitoring of their respective DC power source 602 and 604.Controller 1038 may select a test waveform for use in EIS monitoring forone of the electrochemical devices 602 and 604, and may control therespective inverter 1010 and 1012 of that DC power source 602 and 604 toinject the selected test waveform onto the respective input connection640 and 642. For example, the controller 1038 may send an indication ofthe selected test waveform to the controller 630 of inverter 1010generate the selected test waveform 1002 via pulse width modulation onthe input connection 640 connected to the DC power source 602. Inverter1012 sends offset waveform 1006 to DC power source 604. The inverters1010 and 1012 injecting the test waveform may be configured to monitorthe resulting impedance response of its respective DC power source 602and 604, and via its respective controller 630 and 632 may output anindication of the monitored impedance response to the controller 1038.Continuing with the preceding example, inverter 1010 may monitor theimpedance response on the input connection 640 to the DC power source602 and the controller 630 may indicate the impedance response of DCpower source 602 to the controller 1038.

Controller 1038 may use the impedance response determined by EISmonitoring of an DC power source 602 or 604 to determine acharacteristic of that DC power source 602 or 604 and may adjust asetting of the system 600 based on the determined characteristic. Thecontroller 1038 may compare the impedance response determined by EISmonitoring of an DC power source 602 or 604, such as a plot of theimpedance response and/or stored impedance values, to impedanceresponses stored in a memory, such as stored plots of impedanceresponses and/or stored impedance values, of similar electrochemicaldevices correlated with known characteristics. The controller 1038 maycompare the impedance response determined by EIS monitoring of an DCpower source 602 or 604 to the stored impedance responses in any mannerto identify matches between the impedance responses determined by EISmonitoring of an DC power source 602 or 604 and the stored impedanceresponses.

When the controller 1038 determines a match (e.g., identically or withinsome predetermined variance value) between the impedance responsedetermined by EIS monitoring of a DC power source 602 or 604 and astored impedance response, the controller 1038 may determine thecharacteristic correlated with the stored impedance response to be thecharacteristic of the respective DC power source 602 or 604. Severalexamples are summarized above in the context of FIG. 6.

When a test waveform is injected on an input connection 640 or 642 by arespective inverter 1010 or 1012 to perform EIS monitoring, a ripple onthe respective output connection 620 or 622 may occur. If unaccountedfor, the resulting ripple from the power electronics 610 or 612performing EIS monitoring may cause an undesired ripple on the AC bus1018. To prevent a ripple on the AC bus 1018, the ripple from theinverter 1010 or 1012 performing EIS monitoring may be offset orcanceled by other ripples injected into the AC bus 1018. In anembodiment, the other ripples may be generated by the inverter 1010 or1012 not performing EIS monitoring. The ripples from one or more of theother inverter 1010 or 1012 not performing EIS monitoring may begenerated by controlling the inverter 1010 or 1012 not performing EISmonitoring to inject an offset waveform into their respective inputconnections to their respective input connections 640 or 642. The offsetwaveform or waveforms may be selected by the controller 1038 such thatthe ripples on the respective output connections 620 or 622 generated inresponse to injecting the offset waveform or waveforms cancels theripple caused by the inverter 1010 or 1012 performing EIS monitoringwhen the waveforms are summed at the AC bus 1018. In another embodiment,ripples may be injected into output connections 620 or 622 from devicesother than the inverters 1010 or 1012 to cancel the ripple caused by theinverters 1010 or 1012 performing EIS monitoring when the waveforms aresummed at the AC bus 1018. For example, a waveform generator may beconnected to output connections 620 or 622 to inject canceling ripplesin response to EIS monitoring.

FIG. 10 shows an exemplary test waveform 1002 that may be injected intothe input connection 640 resulting in a ripple 1004 on the outputconnection 620 to the AC bus 1018. An offset waveform 1006 may beinjected into the input connection 642 by the inverter 612 notperforming EIS monitoring resulting in an offset ripple 1008 on theoutput connection 622 to the AC bus 1018. The sum of the ripples 1004and 1008 may be such that an AC voltage 1020 without a ripple occurs onthe AC bus 1018 despite AC ripples 1004 and 1008 occurring on the outputconnections 620 and 622, respectively.

While FIG. 10 shows inverter 1012 providing a single, offset (i.e.,compensating) ripple 1006 in order to cause a net AC voltage 1020without a ripple, it is to be understood that any combination ofinverters in system 1000 may be used to compensate for ripple 1002. Forexample, if system 1000 has a total of four DC power sources (e.g.,similar to system 600 shown in FIG. 9A), then three of the fourinverters may be used to compensate for ripple 1002. Using any othersuitable combination of inverters in the system to generate offsetripples is within the scope of the embodiments.

FIG. 11 illustrates an embodiment method 1100 for canceling the rippleto an AC bus caused by a test waveform using system 1000. In anembodiment, the operations of method 1100 may be performed by acontroller, such as controller 1038.

In block 1102 the controller 1038 may select device DC power source,such as a battery or fuel cell segment, from a plurality of DC powersources for impedance testing. For example, the DC power source may beselected based on a testing protocol governing when and in what order DCpower sources may be tested. In block 1104 the controller 1038 mayselect a test waveform. The test waveform may selected to generatenecessary oscillations for EIS monitoring, such as oscillations ofapproximately 1 Hz.

In block 1106 the controller 1038 may determine a resulting ripple to becaused by the selected test waveform. As discussed above, the resultingripple may be the ripple output to the AC bus from the inverterinjecting the test waveform. In block 1108 the controller 1038 mayidentify the remaining DC power sources. The remaining DC power sourcesmay include batteries, fuel cell stack segments, photovoltaic cells,thermoelectric generators, etc. The remaining DC power sources may bethe DC power sources not selected for impedance testing. In block 1110the controller 1038 may select a portion of the identified remainingelectrochemical devices. In an embodiment, the selected portion may beall identified remaining DC power sources. In another embodiment, theselected portion may be less than all identified remaining DC powersources, such as only a single identified remaining DC power source.

In block 1110 the controller 1038 may determine an offset waveform foreach selected remaining DC power source such that a sum of eachresulting ripple to be caused by the respective determined offsetwaveforms for each selected remaining DC power sources cancels thedetermined resulting ripple to be caused by the selected test waveform.In an embodiment, each offset waveform may be generated such that theresulting ripple is the same, such as one, two, three or more equalripples that together cancel the ripple from the test waveform. Inanother embodiment, each offset waveform may be generated such that theresulting ripples are different, such as two, three, or more differentripples that together cancel the ripple from the test waveform.

In block 1112 the controller 1038 may control the inverter of the DCpower source selected for impedance testing to inject the test waveforminto the selected DC power source. For example, the controller 1038 maysend control signals to a controller (e.g., 1030) of the inverter tocause the inverter to perform pulse width modulation to generate thetest waveform on an input connection to its respective DC power source102. In block 1114 the controller 1038 may control the inverters of eachselected remaining DC power source 102 to inject the offset waveform(e.g., 1032) into each respective DC power source 604. For example, thecontroller 1038 may send control signals to the controllers (e.g., 630or 632) of the inverters to cause the inverters 1030, 1032 to performpulse width modulation to generate the offset waveforms on an inputconnection to their respective DC power source. The operations of method1100 performed in blocks 1112 and 1114 may occur simultaneously, suchthat the test waveform 1002 and offset waveforms 1006 are injected atthe same time resulting in ripples 1004, 1008 that cancel each other outbeing output from the various inverters resulting in the desired ACvoltage 1020 on the AC bus 1018.

In block 1118 the controller 1038 may determine a characteristic of theDC power source 602 selected for impedance testing based at least inpart on the impedance response. As discussed above, the controller mayuse EIS monitoring to plot the real and imaginary parts of the measuredimpedances resulting from the injected test waveform and compare theplotted impedances to the known signatures of impedance responses ofelectrochemical devices with known characteristics. The known signaturesof impedance responses of the electrochemical devices with knowncharacteristics may be stored in a memory available to the controller.The stored known signatures of impedance responses of the DC powersources with known characteristics may be plots of the real andimaginary parts of the measured impedances of healthy DC power sourcesand damaged/degraded DC power sources derived from testing healthy(i.e., undamaged/undegraded) and damaged/degraded DC power sources withvarious forms of damage (e.g., anode cracking for fuel cell systems)and/or degradation (e.g., degradation of the electrolyte for fuel cellsystems). The known characteristics may be correlated with the plots ofthe real and imaginary parts of the measured impedances stored in thememory. By matching the measured impedances to the known signatures ofimpedance responses, the current characteristics or state of the DCpower source may be determined as those characteristics correlated withthe matching known signature of impedance response.

In optional block 1120 the controller 1038 may indicate a failure modebased on the determined characteristic exceeding a failure threshold ofthe DC power source, that a failure mode may be indicated. In optionalblock 1122 the controller 1038 may adjust a setting of the DC powersource system based on the determined characteristic. For example, thecontroller 1038 may adjust (e.g., increase or decrease) drawn currentfrom DC power sources or shut off of the DC power sources based on thedetermined characteristic. In this manner, impedance testing, such asEIS monitoring, may be used to adjust the operation of the DC powersource system based on current characteristics of the DC power sourceusing dedicated inverters for each DC power source.

FIG. 12 is a block diagram of a system 1200 according to an embodiment.FIG. 12 shows system 1200 including two DC power source, such aselectrochemical devices 602 and 604 as part of an array of “n” DC powersources. In the description that follows, merely for the purpose ofillustration, only DC power sources 602 and 604 are discussed. It is tobe understood, however, that system 1200 may include any suitable numberof DC power sources (e.g., the four DC power sources 602, 604, 606, and608 shown in FIG. 6). It is to be further understood that the variousoutput ripples discussed below as being generated by the electricaldevices e.g., DC/DC converters may vary according to the number of DCpower sources.

DC power sources 602 and 604 in system 1200 may be electricallyconnected via a respective input connection 640 and 642 to a respectiveone of DC/DC converters 1210 and 1212. Each input connection 640 and 642may comprise a respective positive input connection 640 a and 642 a aswell as a respective negative input connection 640 b and 642 b. Inoperation, the DC power sources 602 and 604 may output DC voltages totheir respective DC/DC converters 1210 and 1212 via their respectiveinput connections 640 and 642. DC/DC converters 1210 and 1212 may beconnected to inverters 1214 and 1216 via connections 1240 and 1242. Eachconnection 1240 and 1242 may comprise a respective positive inputconnection 1240 a and 1242 a as well as a respective negative inputconnection 1240 b and 1242 b. In operation, DC/DC converters 1210 and1212 may output DC voltages to their respective inverters 1214 and 1216via their respective connections 1240 and 1242.

Note that while FIG. 12 shows each DC/DC converter 1210 and 1212connected individually to different inverters 1214 and 1216, it is to beunderstood that this configuration is merely exemplary. Otherconfigurations are within the scope of the embodiments. For example,system 1200 may include only a single inverter 1214 with each DC/DCconverter connected to the single inverter 1214. A number of othersuitable configurations are possible, including a configuration, forexample, in which groups of DC/DC converters share the same inverter.

The inverters 1214 and 1216 may be connected in parallel to the AC bus1218 by their respective output connections 1220 and 1222. In anembodiment, the AC bus 1218 may be a three phase bus comprised of apositive line 1218 a, a neutral line 1218 b, and a negative line 1218 c,and the respective output connections 1220 and 1222, may includerespective positive output connections 1220 a and 1222 a, respectiveneutral output connections 1220 b and 1222 b, and respective negativeoutput connections 1220 c and 1222 c. In an embodiment, inverters 1214and 1216 may be three phase inverters configured to receive positive andnegative DC inputs from their respective DC/DC converters 1210 and 1212and output positive AC, negative AC, and neutral outputs to the bus 1218via their respective positive output connections 1220 a and 1222 a,respective neutral output connections 1220 b and 1222 b, and respectivenegative output connections 1220 c and 1222 c. In an alternativeembodiment, inverters 1214 and 1216 may each be comprised of dual twophase inverters. The positive output of the first of the two phaseinverters may be connected to the positive line 1218 a of the bus 1218and the negative output of the second of the two phase converters may beconnected to the negative line 1218 c of the bus 1218. The negativeoutput of the first of the two phase inverters and the positive outputof the second of the two phase inverters may be connected together tothe neutral line 1218 b of the bus 1218. One phase or phase invertersmay also be used.

The DC/DC converters 1210 and 1212, may each include controllers 1230and 1232, each controller connected, wired or wirelessly, to centralcontroller 1238. Similarly, inverters 1214 and 1216 may each includecontrollers 1234 and 1236, also connected, wired or wirelessly, tocentral controller 1238. The controllers 1230, 1232, 1234, and 1236 mayinclude processors configured with processor-executable instructions toperform operations to control their respective DC/DC converters 1210 and1212 and inverters 1214 and 1216, and the controller 1238 may be aprocessor configured with processor-executable instructions to performoperations to exchange data with and control the operations of DC/DCconverters 1210 and 1212 and inverters 1214 and 1216 via theirrespective controllers 1230, 1232, 1234, and 1236. The controller 1238may be effectively connected DC/DC converters 1210 and 1212, and controlthe operations of the DC/DC converters 1210 and 1212 via the connectionsA and B between the controllers 1230 and 1232 connected to DC/DCconverters 1210 and 1212 and controller 1238. Similarly The controller1238 may be effectively connected inverters 1214 and 1216, and controlthe operations of inverters 1214 and 1216 via the connections C and Dbetween the controllers 1234 and 1236 connected to inverters 1214 and1216 and controller 1238.

In an embodiment, DC/DC converters 1210 and 1212 may each be configuredto perform EIS monitoring of their respective inverters 1214 and 1216.In particular, DC/DC converters 1210 and 1212 may use EIS to performimpedance testing of capacitors 1214 a and 1216 a included in inverters1214 and 1216, respectively, and shown in the insets in FIG. 12.Capacitors 1214 a and 1216 a may be representative of the effectivecapacitance of multiple components in inverters 1214 and 1216,respectively, rather than single component capacitors.

Controller 1238 may select a test waveform for use in EIS monitoring forone of the inverters 1214 and 1216, and may control DC/DC converters1210 and 1212 to inject the selected test waveform onto the respectiveinverter 1214 and 1216, in particular for testing at least one ofcapacitors 1214 a or 1216 a. For example, the controller 1238 may sendan indication of the selected test waveform to the controller 1230 ofDC/DC converter 1210 to cause opening and closing of a switch at theDC/DC converters 1210 to generate the selected test waveform via pulsewidth modulation on the input connection 1240 connected to the inverter1214. DC/DC converters 1210 and 1212 injecting the test waveform may beconfigured to monitor the resulting impedance response of its respectiveinverter 1214 and 1216, and via its respective controller 1230 or 1232may output an indication of the monitored impedance response to thecontroller 1238. Continuing with the preceding example, DC/DC converter1210 may monitor the impedance response on the input connection 1240 tothe inverter 1214 and the controller 1230 may indicate the impedanceresponse of inverter 1214 to the controller 1238. In particular, theimpedance response may be indicative of an operational state ofcapacitor 1214 a and/or 1216 a. Such an operational state may include,for example, a capacitance range related to the overall functioning ofthe respective inverter 1214 or 1216.

Controller 1238 may use the impedance response determined by EISmonitoring of an inverter 1214 or 1216 to determine a characteristic ofthat inverter 1214 or 1216, or capacitor 1214 a or 1216 a located in therespective inverter, and may adjust a setting of the system 1200 basedon the determined characteristic. The controller 1238 may compare theimpedance response determined by EIS monitoring of an inverter 1214 or1216, such as a plot of the impedance response and/or stored impedancevalues, to impedance responses stored in a memory, such as stored plotsof impedance responses and/or stored impedance values, of similarelectrochemical devices correlated with known characteristics. Thecontroller 1238 may compare the impedance response determined by EISmonitoring of an inverter 1214 or 1216, or capacitor 1214 a or 1216 alocated in the respective inverter, to the stored impedance responses inany manner to identify matches between the impedance responsesdetermined by EIS monitoring of an inverter 1214 or 1216 and the storedimpedance responses. One example of a stored response for comparisonwould be comparing the measured response to a stored response of acapacitor in a properly functioning inverter.

When the controller 1238 determines a match (e.g., identically or withinsome predetermined variance value) between the impedance responsedetermined by EIS monitoring of an inverter 1214 or 1216, or capacitor1214 a or 1216 a located in the respective inverter, and a storedimpedance response, the controller 1238 may determine the characteristiccorrelated with the stored impedance response to be the characteristicof the respective inverter 1214 or 1216, or capacitor 1214 a or 1216 alocated in the respective inverter. The specific EIS measurements areknown. Several examples are summarized above in the context of FIG. 6.

When a test waveform is injected on an input connection 1240 or 1242 bya respective DC/DC converter 1210 or 1212 to perform EIS monitoring, aripple on the respective output connection 1220 or 1222 may occur. Ifunaccounted for, the resulting ripple from the DC/DC converter 1210 or1212 performing EIS monitoring may cause an undesired ripple on the ACbus 1218. To prevent a ripple on the AC bus 1218, the ripple from theDC/DC converter 1210 or 1212 performing EIS monitoring may be offset orcanceled by other ripples injected into the AC bus 1218. In anembodiment, the other ripples may be generated by the DC/DC converter1210 or 1212 not performing EIS monitoring. The ripples from one or moreof the other DC/DC converter 1210 or 1212 not performing EIS monitoringmay be generated by controlling the DC/DC converter 1210 or 1212 notperforming EIS monitoring to inject an offset waveform into theirrespective input connections to their respective input connections 1240or 1242. The offset waveform or waveforms may be selected by thecontroller 1238 such that the ripples on the respective outputconnections 1220 or 1222 generated in response to injecting the offsetwaveform or waveforms cancels the ripple caused by the DC/DC converter1210 or 1212 performing EIS monitoring when the waveforms are summed atthe AC bus 1218. In another embodiment, ripples may be injected intooutput connections 1220 or 1222 from devices other than the DC/DCconverter 1210 or 1212 to cancel the ripple caused by the DC/DCconverter 1210 or 1212 performing EIS monitoring when the waveforms aresummed at the AC bus 1218. For example, a waveform generator may beconnected to output connections 1220 or 1222 to inject canceling ripplesin response to EIS monitoring.

FIG. 12 shows an exemplary test waveform 1202 that may be injected intothe input connection 1240 resulting in a ripple 1204 on the outputconnection 1220 to the AC bus 1218. An offset waveform 1206 may beinjected into the input connection 1242 resulting in an offset ripple1208 on the output connection 1222 to the AC bus 1218. The sum of theripples 1204 and 1208 may be such that an AC voltage 1225 without aripple occurs on the AC bus 1218 despite AC ripples 1204 and 1208occurring on the output connections 1220 and 1222, respectively.

While FIG. 12 shows DC/DC converter 1212 providing a single offsetwaveform 1206 in order to cause a net AC voltage 1225 without a ripple,it is to be understood that any combination of DC/DC converters insystem 1200 may be used to compensate for ripple 1204. For example, ifsystem 1200 has a total of four DC power source (e.g., such as system600 shown in FIG. 9A), then three of the four DC/DC converters may beused to compensate for ripple 1204. Using any other suitable combinationof inverters in the system to generate offset ripples is within thescope of the embodiments.

FIG. 13 illustrates an embodiment method 1300 for EIS testing of acapacitor in an inverter and canceling the ripple to an AC bus caused bya test waveform using system 1200. In an embodiment, the operations ofmethod 1300 may be performed by a controller, such as controller 1238.The operations of method 1300 are discussed in terms of inverters,capacitors, batteries, and fuel cell stack segments, but inverters,capacitors, batteries, and fuel cell stack segments are used merely asexamples. Other electrochemical devices and/or other power electronicsmay be used in the various operations of method 1300.

In block 1302 the controller 1238 may select an inverter, from aplurality of inverters, for impedance testing. For example, the invertermay be selected based on a testing protocol governing when and in whatorder inverters may be tested. The inverter for testing may also beselected based on indications that capacitors within the inverter aremalfunctioning or are in need of diagnostic (e.g., based on a predictedlifetime for the capacitor, etc.). Still other ways of selecting theinverter for testing include obtaining a measured response indicative ofinverter malfunction (e.g., unexpected variations in output voltage orcurrent).

In block 1304 the controller 1238 may select a test waveform. The testwaveform may selected to generate necessary oscillations for EISmonitoring, such as oscillations of approximately 1 Hz. The test waveform is to be provided to the inverter via its respective DC/DCconverter, for example provided to inverter 1214 via its adjacent DC/DCconverter 1210, as shown in FIG. 12.

In block 1306 the controller 1238 may determine a resulting ripple to becaused by the selected test waveform. As discussed above, the resultingripple may be the ripple output to the AC bus from the inverter intowhich the test waveform was injected. In block 1308 the controller 1238may identify the remaining devices not subject to testing. Theseremaining devices may include inverters and DC/DC converters not subjectto EIS testing. The remaining devices may also include other devices,e.g., capacitors, supercapacitors, batteries, and fuel cell stacksegments. In block 1309 the controller 1238 may select a portion of theidentified remaining devices. In an embodiment, the selected portion maybe, for example, all identified remaining DC/DC converters andinverters. In another embodiment, the selected portion may be less thanall identified remaining DC/DC converters and inverters, such as only asingle identified remaining DC/DC converters and inverters. In stillanother embodiment, the selected portion may include any one or more ofDC/DC converters, inverters, supercapacitors, capacitors, batteries, andfuel cell stack segments.

In block 1310 the controller 1238 may determine an offset waveform foreach selected remaining device such that a sum of each resulting rippleto be caused by the respective determined offset waveforms for eachselected remaining device cancels the determined resulting ripple to becaused by the selected test waveform. In an embodiment, each offsetwaveform may be generated such that the resulting ripple is the same,such as one, two, three or more equal ripples that together cancel theripple from the test waveform. In another embodiment, each offsetwaveform may be generated such that the resulting ripples are different,such as two, three, or more different ripples that together cancel theripple from the test waveform.

In block 1312 the controller 1238 may control the DC/DC converter of therespective inverter selected for impedance testing to inject the testwaveform into the selected inverter. For example, the controller 1238may send control signals to a controller (e.g., 1230 or 1232) of theinverter to cause the converter to perform pulse width modulation togenerate the test waveform on an input connection to the inverter. Inblock 1314 the controller 1238 may control the selected remainingdevices to inject the offset waveform for each selected remaininginverters into each respective inverters. For example, the controller1238 may send control signals to the controllers (e.g., 1230 or 1232) ofthe DC/DC converters to cause the converters to perform pulse widthmodulation to generate the offset waveforms on an input connection totheir respective inverters. The operations of method 1300 performed inblocks 1312 and 1314 may occur simultaneously, such that the testwaveform and offset waveforms are injected at the same time resulting inripples being output from the various Inverters that cancel each otherout resulting in a the desired AC voltage on the AC bus.

In block 1316 the controller 1238 may determine a characteristic of theinverter selected for impedance testing based at least in part on theimpedance response. As discussed above, the controller may use EISmonitoring to plot the real and imaginary parts of the measuredimpedances resulting from the injected test waveform and compare theplotted impedances to the known signatures of impedance responses ofinverters or capacitors with known characteristics. The known signaturesof impedance responses of the of inverters or capacitors with knowncharacteristics may be stored in a memory available to the controller.The stored known signatures of impedance responses of the of invertersor capacitors with known characteristics may be plots of the real andimaginary parts of the measured impedances of healthy of inverters orcapacitors and damaged/degraded of inverters or capacitors derived fromtesting healthy (i.e., undamaged/undegraded) and damaged/degraded ofinverters or capacitors with various forms of damage (e.g., anodecracking) and/or degradation of capacitance. The known characteristicsmay be correlated with the plots of the real and imaginary parts of themeasured impedances stored in the memory.

By matching the measured impedances to the known signatures of impedanceresponses, the current characteristics or state of the inverter or itscapacitor may be determined as those characteristics correlated with thematching known signature of impedance response. In optional block 1318the controller 1238 may indicate a failure mode based on the determinedcharacteristic exceeding a failure threshold. For example, if thedetermined characteristic exceeds a failure threshold a failure mode ofan inverter or a capacitor a failure state may be indicated. In optionalblock 1320 the controller 1238 may adjust a setting of the inverter orthe entire system based on the determined characteristic. For example,the controller 1238 may adjust (e.g., increase or decrease) drawncurrent from DC/DC converters to specific inverters or shut off of theDC/DC converters and their corresponding inverters based on thedetermined characteristic. In this manner, impedance testing, such asEIS monitoring, may be used to adjust the operation of the inverterbased on current characteristics of the and inverter.

In summary, in one embodiment described above with respect to FIGS.9A-9C, a system includes a direct current (“DC”) bus, a first DC powersource other than a fuel cell electrically connected via a first inputconnection to a first DC converter, wherein the first DC converter isconnected via a first output connection to the DC bus, at least onesecond DC power source other than a fuel cell electrically connected viaat least one second input connection to at least one second DCconverter, wherein the at least one second DC converter is connected viaat least second output connection to the DC bus and wherein the firstoutput connection and the at least one second output connection connectthe first DC converter and the at least one second DC converter to theDC bus in parallel and a processor connected to the first DC converterand the at least one second DC converter.

The processor is configured with processor-executable instructions toperform operations comprising selecting a test waveform to inject ontothe first input connection from the first DC converter to the first DCpower source other than a fuel cell, determining a first resultingripple on the first output connection that will be generated in responseto injecting the test waveform onto the first input connection,determining at least one offset waveform to inject onto the at least onesecond input connection from the at least one second DC converter to theat least one second DC power source other than a fuel cell such that oneor more second ripples which will be provided to the at least one secondoutput connection cancel the first resulting ripple, controlling thefirst DC converter to inject the test waveform onto the first inputconnection, and controlling the at least one second DC converter toinject the at least one offset waveform onto the at least one secondinput connection.

In one embodiment, at least one of the first DC power source other thana fuel cell and the at least one second DC power source other than afuel cell each comprises at least one battery. In another embodiment,the at least one second DC power source other than a fuel cell comprisesan electrolysis cell or an electrochemical pumping cell. In yet anotherembodiment, the at least one second DC power source other than a fuelcell comprises a supercapacitor, a photovoltaic device or athermoelectric device.

In one embodiment, the processor is configured with processor-executableinstructions to perform operations further comprising controlling thefirst DC converter to monitor an impedance response of the first DCpower source other than a fuel cell using impedance spectroscopy (“EIS”)in response to the injected test waveform, and determining acharacteristic of the first DC power source other than a fuel cell basedat least in part on the impedance response of the first DC power sourceother than a fuel cell. The processor may also be configured withprocessor-executable instructions to perform operations furthercomprising adjusting a setting of the first DC power source other than afuel cell based on the determined characteristic. The determinedcharacteristic may be one of a battery capacity, a battery state ofcharge (SoC), a battery state of health (SoH), and an overall batterylifetime. Adjusting a setting of the first DC power source other than afuel cell may comprise adjusting a charging state of the first DC powersource other than a fuel cell.

In another embodiment, the processor is configured withprocessor-executable instructions to perform operations furthercomprising determining whether the determined characteristic exceeds afailure threshold, and indicating a failure mode in response todetermining the determined characteristic exceeds the failure threshold.The failure threshold may indicate a decreased battery capacity of thefirst DC power source other than a fuel cell and the failure modeincludes decreasing power drawn from the first DC power source otherthan a fuel cell.

Furthermore, in the embodiment described above with respect to FIGS.9A-9C, a method comprises selecting a test waveform to inject from afirst DC converter to at least one first DC power source other than afuel cell, determining a first resulting ripple that will be generatedin response to injecting the test waveform onto the battery, determiningat least one offset waveform to inject from at least one second DCconverter to at least one second DC power source to generate one or moresecond ripples which cancel the first resulting ripple, injecting thetest waveform from the first DC converter to the at least one first DCpower source, injecting the at least one offset waveform from the atleast one second DC converter to the at least one second DC powersource, and determining a characteristic of the first DC power sourcebased at least in part on the impedance response of the first DC powersource.

In one embodiment, the at least one first DC power source other than afuel cell comprises a battery. Determining the characteristic of thefirst DC power source may comprise determining if the battery ischarging or discharging. Determining if the battery is charging ordischarging may comprise determining that the battery is charging if themeasurement indicates that the first resulting ripple has beencancelled, and determining that the battery is discharging if themeasurement indicates that the first resulting ripple has not beencancelled. In one embodiment, determining the characteristic of thefirst DC power source comprises determining at least one of a batterycapacity, a battery state of charge (SoC), a battery state of health(SoH), and an overall battery lifetime.

In another embodiment described above with respect to FIGS. 10 and 11, asystem comprises an alternating current (“AC”) bus, a first directcurrent (“DC”) power source electrically connected via a first inputconnection to a first inverter, wherein the first inverter is connectedvia a first output connection to the AC bus, at least one second DCpower source electrically connected via at least one second inputconnection to at least one second inverter, wherein the at least onesecond inverter is connected via at least second output connection tothe AC bus and wherein the first output connection and the at least onesecond output connection connect the first inverter and the at least onesecond inverter to the AC bus in parallel, and a processor connected tothe first inverter and the at least one second inverter.

The processor is configured with processor-executable instructions toperform operations comprising selecting a test waveform to inject ontothe first input connection from the first inverter to the first DC powersource, determining a first resulting ripple on the first outputconnection that will be generated in response to injecting the testwaveform onto the first input connection, determining at least oneoffset waveform to inject onto the at least one second input connectionfrom the at least one second inverter to the at least one second DCpower source such that one or more second ripples which will be providedto the at least one second output connection cancel the first resultingripple, controlling the first inverter to inject the test waveform ontothe first input connection, and controlling the at least one secondinverter to inject the at least one offset waveform onto the at leastone second input connection.

In one embodiment, the processor is configured with processor-executableinstructions to perform operations further comprising controlling thefirst inverter to monitor a first impedance response of the first DCpower source using impedance spectroscopy (“EIS”) in response to theinjected first test waveform, and determining a characteristic of thefirst DC power source based at least in part on the first impedanceresponse of the first DC power source. The first DC power source maycomprise at least one of a fuel cell stack, an electrolysis cell, anelectrochemical pumping cell, a battery, a supercapacitor, aphotovoltaic device or a thermoelectric device, and the processor may beconfigured with processor-executable instructions to perform operationsfurther comprising adjusting a setting of the first DC power sourcebased on the determined characteristic. In one embodiment, the first DCpower source comprises the battery, the determined characteristic is oneof a battery capacity, a battery state of charge (SoC), a battery stateof health (SoH), and an overall battery lifetime, and adjusting asetting of the first DC power source comprises adjusting a chargingstate of the first DC power source.

In another embodiment, the processor is configured withprocessor-executable instructions to perform operations furthercomprising determining whether the determined characteristic exceeds afailure threshold, and indicating a failure mode in response todetermining the determined characteristic exceeds the failure threshold.

In another embodiment described above with respect to FIGS. 12 and 13, asystem comprises an alternating current (“AC”) bus, a first directcurrent (“DC”) power source electrically connected via a first DC powersource input connection to a first DC converter, a first inverterconnected to the first DC converter via a first DC converter outputconnection and connected to the AC bus via a first inverter outputconnection, and a processor connected to the first DC converter. Theprocessor is configured with processor-executable instructions toperform operations comprising selecting a test waveform to inject ontothe first DC converter output connection from the first DC converter tothe first inverter, controlling the first DC converter to inject thetest waveform onto the first DC converter output connection, andmeasuring a response from the inverter to the test waveform.

In one embodiment, the processor is further configured to performoperations comprising relating the measured response to an operationalstate of one or more capacitors in the first inverter. The operationalstate may include at least one of a capacitance range related to theoverall functioning of the inverter, a predicted lifetime of thecapacitor, or a capacitance of the capacitor. In one embodiment,relating the measured response to an operational state of one or morecapacitors comprises comparing the measured response to a storedresponse of a capacitor in a properly functioning inverter.

According to another embodiment described above with respect to FIGS.9A-9E, a system includes a direct current (“DC”) bus, a batteryelectrically connected via a first input connection to a first DCconverter, wherein the first DC converter is connected via a firstoutput connection to the DC bus, at least one second DC power sourceelectrically connected via at least one second input connection to atleast one second DC converter, wherein the at least one second DCconverter is connected via at least second output connection to the DCbus and wherein the first output connection and the at least one secondoutput connection connect the first DC converter and the at least onesecond DC converter to the DC bus in parallel, and a processor connectedto the first DC converter and the at least one second DC converter. Theprocessor is configured with processor-executable instructions toperform operations comprising selecting a test waveform to inject ontothe first input connection from the first DC converter to the battery,determining a first resulting ripple on the first output connection thatwill be generated in response to injecting the test waveform onto thefirst input connection, determining at least one offset waveform toinject onto the at least one second input connection from the at leastone second DC converter to the at least one second DC power source suchthat one or more second ripples which will be provided to the at leastone second output connection will cancel the first resulting ripple ifthe battery is charging, controlling the first DC converter to injectthe test waveform onto the first input connection, controlling the atleast one second DC converter to inject the at least one offset waveformonto the at least one second input connection, measuring an output onthe first DC converter output connection, and determining if the batteryis charging or discharging based on the measured output.

In one embodiment, determining if the battery is charging or dischargingcomprises determining that the battery is charging if the measurementindicates that the first resulting ripple has been cancelled, anddetermining that the battery is discharging if the measurement indicatesthat the first resulting ripple has not been cancelled.

In another embodiment, the operations further comprise monitoring animpedance response of the battery using electrochemical impedancespectroscopy (“EIS”) in response to the injected test waveform, anddetermining a characteristic of the battery based at least in part onthe impedance response of the battery. The operations may furthercomprise adjusting a setting of the battery based on the determinedcharacteristic. The determined characteristic may be one of a batterycapacity, a battery state of charge (SoC), a battery state of health(SoH), and an overall battery lifetime, and the operations may furthercomprise adjusting a setting of the battery comprises adjusting acharging state of the battery.

In another embodiment, the operations further comprise determiningwhether the determined characteristic exceeds a failure threshold, andindicating a failure mode in response to determining the determinedcharacteristic exceeds the failure threshold. The failure threshold mayindicates a decreased battery capacity of the battery and the operationsmay further comprise decreasing power drawn from the battery in responseto the indication of the failure mode. The at least one second DC powersource may comprise a battery, at least one fuel cell stack segment,electrolysis cells, or electrochemical pumping cells.

In the embodiment described above with respect to FIGS. 9A-9E, a methodincludes selecting a test waveform to inject to a battery from a firstDC converter, determining a first resulting ripple that will begenerated in response to injecting the test waveform, determining atleast one offset waveform to inject to at least one second DC powersource from at least one second DC converter such that one or moresecond ripples will be provided that will cancel the first resultingripple if the battery is charging, injecting the test waveform to thebattery, injecting the at least one offset waveform to the at least onesecond DC power source, determining if the first resulting ripple hasbeen cancelled, and determining if the battery is charging ordischarging based on the step of determining if the first resultingripple has been cancelled.

In one embodiment, determining if the first resulting ripple has beencancelled comprises determining that the battery is charging if thefirst resulting ripple has been cancelled, and determining that thebattery is discharging if the first resulting ripple has not beencancelled.

In one embodiment, the method further comprises monitoring an impedanceresponse of the battery using electrochemical impedance spectroscopy(“EIS”) in response to the injected test waveform, and determining acharacteristic of the battery based at least in part on the impedanceresponse of the battery. The method may further comprise adjusting asetting of the battery based on the determined characteristic. Thedetermined characteristic may be one of a battery capacity, a batterystate of charge (SoC), a battery state of health (SoH), and an overallbattery lifetime, and adjusting a setting of the battery may compriseadjusting a charging state of the battery.

In another embodiment, the method further comprises determining whetherthe determined characteristic exceeds a failure threshold, andindicating a failure mode in response to determining the determinedcharacteristic exceeds the failure threshold. The failure threshold mayindicate a decreased battery capacity of the battery, and the method mayfurther comprise decreasing power drawn from the battery in response tothe indication of the failure mode. The at least one second DC powersource may comprise a battery, at least one fuel cell stack segment,electrolysis cells, or electrochemical pumping cells.

One or more diagrams have been used to describe exemplary embodiments.The use of diagrams is not meant to be limiting with respect to theorder of operations performed. The foregoing description of exemplaryembodiments has been presented for purposes of illustration and ofdescription. It is not intended to be exhaustive or limiting withrespect to the precise form disclosed, and modifications and variationsare possible in light of the above teachings or may be acquired frompractice of the disclosed embodiments. It is intended that the scope ofthe invention be defined by the claims appended hereto and theirequivalents.

Control elements may be implemented using computing devices (such ascomputer) comprising processors, memory and other components that havebeen programmed with instructions to perform specific functions or maybe implemented in processors designed to perform the specifiedfunctions. A processor may be any programmable microprocessor,microcomputer or multiple processor chip or chips that can be configuredby software instructions (applications) to perform a variety offunctions, including the functions of the various embodiments describedherein. In some computing devices, multiple processors may be provided.Typically, software applications may be stored in the internal memorybefore they are accessed and loaded into the processor. In somecomputing devices, the processor may include internal memory sufficientto store the application software instructions.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentinvention.

The hardware used to implement the various illustrative logics, logicalblocks, modules, and circuits described in connection with the aspectsdisclosed herein may be implemented or performed with a general purposeprocessor, a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA) orother programmable logic device, discrete gate or transistor logic,discrete hardware components, or any combination thereof designed toperform the functions described herein. A general-purpose processor maybe a microprocessor, but, in the alternative, the processor may be anyconventional processor, controller, microcontroller, or state machine. Aprocessor may also be implemented as a combination of computing devices,e.g., a combination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration. Alternatively, some blocks ormethods may be performed by circuitry that is specific to a givenfunction.

The preceding description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the describedembodiment. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thescope of the disclosure. Thus, the present invention is not intended tobe limited to the embodiments shown herein but is to be accorded thewidest scope consistent with the following claims and the principles andnovel features disclosed herein.

What is claimed is:
 1. A system of, comprising: a direct current (“DC”) bus; a first DC power source other than a fuel cell electrically connected via a first input connection to a first DC converter, wherein the first DC converter is connected via a first output connection to the DC bus; at least one second DC power source other than a fuel cell electrically connected via at least one second input connection to at least one second DC converter, wherein the at least one second DC converter is connected via at least one second output connection to the DC bus and wherein the first output connection and the at least one second output connection connect the first DC converter and the at least one second DC converter to the DC bus in parallel; and a processor connected to the first DC converter and the at least one second DC converter, wherein the processor is configured with processor-executable instructions to perform operations comprising: selecting a test waveform to inject onto the first input connection from the first DC converter to the first DC power source other than a fuel cell; determining a first resulting ripple on the first output connection that will be generated in response to injecting the test waveform onto the first input connection; determining at least one offset waveform to inject onto the at least one second input connection from the at least one second DC converter to the at least one second DC power source other than a fuel cell such that one or more second ripples which will be provided to the at least one second output connection to cancel the first resulting ripple; controlling the first DC converter to inject the test waveform onto the first input connection; and controlling the at least one second DC converter to inject the at least one offset waveform onto the at least one second input connection; wherein at least one of the first DC power source other than a fuel cell and the at least one second DC power source other than a fuel cell each comprises at least one battery; wherein the processor is configured with processor-executable instructions to perform operations further comprising: controlling the first DC converter to monitor an impedance response of the first DC power source other than a fuel cell using impedance spectroscopy (“EIS”) in response to the injected test waveform; determining a characteristic of the first DC power source other than a fuel cell based at least in part on the impedance response of the first DC power source other than a fuel cell; and adjusting a setting of the first DC power source other than a fuel cell based on the determined characteristic; wherein: the determined characteristic is one of a battery capacity, a battery state of charge (SoC), a battery state of health (SoH), and an overall battery lifetime; and adjusting a setting of the first DC power source other than a fuel cell comprises adjusting a charging state of the first DC power source other than a fuel cell.
 2. A system, comprising: a direct current (“DC”) bus; a first DC power source other than a fuel cell electrically connected via a first input connection to a first DC converter, wherein the first DC converter is connected via a first output connection to the DC bus; at least one second DC power source other than a fuel cell electrically connected via at least one second input connection to at least one second DC converter, wherein the at least one second DC converter is connected via at least one second output connection to the DC bus and wherein the first output connection and the at least one second output connection connect the first DC converter and the at least one second DC converter to the DC bus in parallel; and a processor connected to the first DC converter and the at least one second DC converter, wherein the processor is configured with processor-executable instructions to perform operations comprising: selecting a test waveform to inject onto the first input connection from the first DC converter to the first DC power source other than a fuel cell; determining a first resulting ripple on the first output connection that will be generated in response to injecting the test waveform onto the first input connection; determining at least one offset waveform to inject onto the at least one second input connection from the at least one second DC converter to the at least one second DC power source other than a fuel cell such that one or more second ripples which will be provided to the at least one second output connection to cancel the first resulting ripple; controlling the first DC converter to inject the test waveform onto the first input connection; and controlling the at least one second DC converter to inject the at least one offset waveform onto the at least one second input connection; wherein at least one of the first DC power source other than a fuel cell and the at least one second DC power source other than a fuel cell each comprises at least one battery; wherein the processor is configured with processor-executable instructions to perform operations further comprising: controlling the first DC converter to monitor an impedance response of the first DC power source other than a fuel cell using impedance spectroscopy (“EIS”) in response to the injected test waveform; and determining a characteristic of the first DC power source other than a fuel cell based at least in part on the impedance response of the first DC power source other than a fuel cell: determining whether the determined characteristic exceeds a failure threshold; and indicating a failure mode in response to determining the determined characteristic exceeds the failure threshold; and wherein the failure threshold indicates a decreased battery capacity of the first DC power source other than a fuel cell and the failure mode includes decreasing power drawn from the first DC power source other than a fuel cell.
 3. The system of claim 2, wherein the at least one second DC power source other than a fuel cell comprises an electrolysis cell or an electrochemical pumping cell.
 4. The system of claim 2, wherein the at least one second DC power source other than a fuel cell comprises a supercapacitor, a photovoltaic device or a thermoelectric device.
 5. A system, comprising: an alternating current (“AC”) bus; a first direct current (“DC”) power source electrically connected via a first input connection to a first inverter, wherein the first inverter is connected via a first output connection to the AC bus; at least one second DC power source electrically connected via at least one second input connection to at least one second inverter, wherein the at least one second inverter is connected via at least one second output connection to the AC bus and wherein the first output connection and the at least one second output connection connect the first inverter and the at least one second inverter to the AC bus in parallel; and a processor connected to the first inverter and the at least one second inverter, wherein the processor is configured with processor-executable instructions to perform operations comprising: selecting a test waveform to inject onto the first input connection from the first inverter to the first DC power source; determining a first resulting ripple on the first output connection that will be generated in response to injecting the test waveform onto the first input connection; determining at least one offset waveform to inject onto the at least one second input connection from the at least one second inverter to the at least one second DC power source such that one or more second ripples which will be provided to the at least one second output connection to cancel the first resulting ripple; controlling the first inverter to inject the test waveform onto the first input connection; and controlling the at least one second inverter to inject the at least one offset waveform onto the at least one second input connection.
 6. The system of claim 5, wherein the processor is configured with processor-executable instructions to perform operations further comprising: controlling the first inverter to monitor a first impedance response of the first DC power source using impedance spectroscopy (“EIS”) in response to the injected first test waveform; and determining a characteristic of the first DC power source based at least in part on the first impedance response of the first DC power source.
 7. The system of claim 6, wherein: the first DC power source comprises at least one of a fuel cell stack, an electrolysis cell, an electrochemical pumping cell, a battery, a supercapacitor, a photovoltaic device or a thermoelectric device; and the processor is configured with processor-executable instructions to perform operations further comprising adjusting a setting of the first DC power source based on the determined characteristic.
 8. The system of claim 7, wherein: the first DC power source comprises the battery; the determined characteristic is one of a battery capacity, a battery state of charge (SoC), a battery state of health (SoH), and an overall battery lifetime; and adjusting a setting of the first DC power source comprises adjusting a charging state of the first DC power source.
 9. The system of claim 6, wherein the processor is configured with processor-executable instructions to perform operations further comprising: determining whether the determined characteristic exceeds a failure threshold; and indicating a failure mode in response to determining the determined characteristic exceeds the failure threshold.
 10. A system of, comprising: an alternating current (“AC”) bus; a first direct current (“DC”) power source electrically connected via a first DC power source input connection to a first DC converter; a first inverter connected to the first DC converter via a first DC converter output connection and connected to the AC bus via a first inverter output connection; and a processor connected to the first DC converter, wherein the processor is configured with processor-executable instructions to perform operations comprising: selecting a test waveform to inject onto the first DC converter output connection from the first DC converter to the first inverter; controlling the first DC converter to inject the test waveform onto the first DC converter output connection; measuring a response from the inverter to the test waveform; and relating the measured response to an operational state of one or more capacitors in the first inverter; and wherein the operational state includes at least one of a capacitance range related to the overall functioning of the inverter, a predicted lifetime of the capacitor, or a capacitance of the capacitor.
 11. A system of, comprising: an alternating current (“AC”) bus; a first direct current (“DC”) power source electrically connected via a first DC power source input connection to a first DC converter; a first inverter connected to the first DC converter via a first DC converter output connection and connected to the AC bus via a first inverter output connection; and a processor connected to the first DC converter, wherein the processor is configured with processor-executable instructions to perform operations comprising: selecting a test waveform to inject onto the first DC converter output connection from the first DC converter to the first inverter; controlling the first DC converter to inject the test waveform onto the first DC converter output connection; measuring a response from the inverter to the test waveform; and relating the measured response to an operational state of one or more capacitors in the first inverter; and wherein relating the measured response to an operational state of one or more capacitors comprises comparing the measured response to a stored response of a capacitor in a properly functioning inverter.
 12. A method of, comprising: selecting a test waveform to inject from a first DC converter to at least one first DC power source other than a fuel cell; determining a first resulting ripple that will be generated in response to injecting the test waveform onto a battery; determining at least one offset waveform to inject from at least one second DC converter to at least one second DC power source to generate one or more second ripples which cancel the first resulting ripple; injecting the test waveform from the first DC converter to the at least one first DC power source: injecting the at least one offset waveform from the at least one second DC converter to the at least one second DC power source; and determining a characteristic of the first DC power source based at least in part on an impedance response of the first DC power source; wherein the at least one first DC power source other than a fuel cell comprises a battery; wherein determining the characteristic of the first DC power source comprises determining if the battery is charging or discharging; and wherein determining if the battery is charging or discharging comprises: determining that the battery is charging if the measurement indicates that the first resulting ripple has been cancelled; and determining that the battery is discharging if the measurement indicates that the first resulting ripple has not been cancelled.
 13. The method of claim 12, wherein determining the characteristic of the first DC power source comprises determining at least one of a battery capacity, a battery state of charge (SoC), a battery state of health (SoH), and an overall battery lifetime. 